SDM Stage 1 persists (consistent with a La-Nina composite), with tropospheric relative AAM still ~2 standard deviations below the 1979-1998 climatology. The upper tropospheric pattern across the PNA sector continues to respond with an east Asian trough-central Pacific ridge (with a subtropical low to the south as part of split-flow configuration)-east Pacific/west coast USA trough. Tropical convective forcing remains strong centered ~5S/110E with weekly mean anomalies of at least minus 50-70 w/m**2. Please see the following links:
http://www.cdc.noaa.gov/map/images/olr/olr.alt.anom.gif
http://www.ssec.wisc.edu/data/geo/mtsat/
In the following, I will fill in some of the details of our current weather-climate situation. Afterwards, a few insights into the future (weeks 1-3) for primarily the weather across the CONUS is offerred.
Equatorial SSTs remain cooler than normal from ~160E to just west of the South American coast with magnitudes as low as ~minus 2C around 110W extending to depths of at least 200m. The warming along the immediate coast of South America may be related to the seasonal cycle. Comparable warmth is still observed just west of the date line and particularly over the subtropical South Pacific Ocean. Time-longitude plots of SSTAs do indicate some very slight eastward shifting of the negative anomalies across the equatorial cold tongue during the last 2-3 weeks. This may be linked to recent surface westerly wind anomalies from the IO/Indonesian tropical convection. Only time will tell if there is any importance to this behavior. Links below provide more detailed SST information.
http://www.pmel.noaa.gov/tao/jsdisplay/
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
As discussed in many of my previous postings and pointed out by others including CPC, this SST distribution does project onto a La-Nina composite (matches up spatially).
Tropical convection is currently concentrated ~5S/110E, and extends from the central IO across Indonesia, with weaker storm clusters east-southeast to near Polynesia. Tropical cyclone Glenda was located just northwest of Australia at the time of this writing (see http://severe.worldweather.org/tc/au/, http://www.npmoc.navy.mil/jtwc.html for details). As shown by the coherent modes Hovmoller plots to isolate tropical convective variability via time filtering (link below), after a consolidation about 7-10 days ago, some eastward movement has been occuring. There is a projection onto a weak MJO, and a back of the envelope phase speed computation gives me ~3-4 m/s. Whether or not it is a MJO, we will see. My own thought is we are seeing another 20-30 day mode that has dynamic linkages to the extratropics via subtropical wavetrains. One response to all this convection has been enhanced trade winds to its east and westerlies across the tropical IO and Indonesia, with anomalies ~5-10m/s contributing to above average low-level convergence (part of a positive feedback mechanism).
http://www.cdc.noaa.gov/map/clim/olr_modes/
Recent full-disk satellite imagery has also revealed some flare-ups along both the North and South Pacific ITCZs (NITCZ and SITCZ, respectively). Interactions with the subtropics downstream from the twin upper tropospheric subtropical cyclones (discussed below) may be a contributor. The NITCZ has allowed a moist STJ to extend into Mexico and the Gulf of Mexico.
Finally, intense frontal and diurnal thunderstorm activity persists across northern South America and Brasil. This activity has been supporting STJs acros the Atlantic.
http://www.ssec.wisc.edu/data/
Animations of fields such as 150mb and 250mb daily mean vector wind anomalies (link given below) reveal the general SDM Stage 1 circulation pattern currently featuring twin subtropical anticyclones across mainly the region of Indonesia with downstream twin subtropical cyclones east of the date line (leading to split flow across the North Pacific -- ridge to the north of low). The northern member of these twin lows has been pounding Hawaii with excessive rainfall for at least the past 2-3 weeks, while also maintaining a moist STJ linked to South Pacific convection into the southwestern USA. Additionally, there have been synoptic events involving both baroclinic wave packets and fast RWDs, with "wave packet envelopes" circling the globe about once/every 8-10 days. Time-longitude plots reveal an essentially stationary zonal wave number 5-6 pattern across the subtropics (10-40N) with oscillations between waves 3-5 to the north (30-60N) since roughly mid February. Tied to all of this has been a general negative phase of the PNA teleconnection and "bursting" central Pacific anticyclones into the Arctic leading to projections onto the negative phases of both the AO and NAO (and possibly leading to the final warming of the northern stratosphere).
http://www.cdc.noaa.gov/map/clim/glbcir.anim.shtml
Time-latitude sections of upper tropospheric zonal mean zonal wind anomalies still present a general meridional symmetry (typical of strongly forced situations from the tropics). While zonal mean anomalous easterlies still persist north of 60, the magnitudes have weakened to ~minus 5 m/s. Anomalous westerly flow continues around 30N, while also increasing throughout equatorial and northern subtropical atmospheres. Animations suggest the latter is tied to the recent eastward movement of the tropical forcing (discussed above). Hence global relative AAM has been increasing for about the past week, from a low of ~minus 3.5 standard deviations to about minus 2 (1979-1998 climatology - see link below)
http://www.cdc.noaa.gov/map/images/aam/glaam.gif
As seen from the plot, in terms of a vertical and zonal average much of the global increase has been from the removal of anomalous easterly flow throughout the northern subtropics.
Model performance has been improving during the last few days (see links below), after a recent drop linked to the IO tropical convective flare-up about 7-10 days ago. However, given the split-flow pattern across the North Pacific and the liklihood of more tropical convective bursts (in addition to seasonal transition), models may continue to struggle.
http://www.emc.ncep.noaa.gov/
http://wwwt.emc.ncep.noaa.gov/gmb/para/paralog.t170fcst.html
http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_nh.html
Where the atmosphere goes from here is always a good question. However, I think our SDM Stage 1 state is most probable for at least the next 10-14 days. Depending how far east the tropical convection moves, Stage 2 may be possible late week 2 into week 3. Most models (links to 2 of them below) are now capturing the signal for another strong baroclinic storm development initially impacting the USA west coast late this weekend, then moving into the Rockies leading to possibly intense baroclinic development on the Plains by ~middle of next week (days 7-8). That is consistent with the previous (botched) Blog posting on March 26th, and I would agree. An important but transient trough may also deepen across particulary the east and northeast states as well (large amplitude pattern) early-mid next week. For week 2 I think at least one more strong trough (relative to climatology) is probable for the western and central states. Should Stage 2 evolve, troughs may initially impact the Rockies late week 2 into week 3 instead of the USA west coast.
http://www.emc.ncep.noaa.gov/gmb/ens/targ/hgtmenu.html
http://www.cdc.noaa.gov/map/images/ens_jsw/ens_jsw.html
Active weather is likely to rule most of the country through week 2. As mentioned before, thanks to La-Nina, a climatologically active time of the year is being enhanced. The storm track may remain slightly south of normal, extending from the southwest states into the Great Lakes and Ohio Valley. Probable impacts include late season winter storm concerns from the Rockies into the perhaps the Upper Mississippi Valley, with severe local storms and excessive rainfall from the Central/Southern Plains into the Ohio Valley. Parts of the country that have been dry (eastern states, Southern Plains, etc.) should see at least some needed precipitation.
Same story remains for southwest Kansas. At least some opportunities of precipitation are currently presenting themselves. However, most will remain to the east, north and southeast due to the problem of dry intrusions, etc., with each passing low. Some precipitation looks reasonable for this upcoming weekend with perhaps more around the middle of next week. Opportunities of precipitation should continue to present themselves week 2. Temperatures will probably tilt toward above normal for the next 1-2 weeks.
I will try to do another update this weekend.
Ed Berry
Wednesday, March 29, 2006
Sunday, March 26, 2006
The Atmosphere is Stuck
A writing that I had ready to post was lost by this Blogger, despite saving the drafts (about 2 hours of work!). The intent was to be an update to the posting on March 23rd. In any case, what was discussed on my last posting is still valid. I wanted to make a point about the loss of predictability in many of the models tied to the recent tropical convective flare-up across the IO. That can be seen from looking at the skill scores available from http://www.emc.ncep.noaa.gov/ . Research work shows that loss of model skill will occur during situations when the tropical convective forcing changes abruptly during a forecast cycle; not only for week 2, but even for days 3-7 at times.
I am not going to repeat what I just lost. SDM Stage 1 is most probable for at least the next 2 weeks, with possibly Stage 2 by week 3 should the EH tropical convective forcing (currently ~centered 0/110E with weaker thunderstorm clusters across the west Pacific) move far enough to the east (to ~150E). An active weather pattern is likely for particularly the western and central parts of the country (USA), with synoptic-scale baroclinic troughs about every 3-5 days. I have a thought of a particularly strong cyclonic development during week 2 affecting the Rockies and Plains with all relevant high-impact weather concerns (see March 23 Blog for details). In some sense, we may be seeing an enhancement of our spring-time climatology, which is not unusual for a La-Nina.
Nothing different for me to offer for southwest Kansas weather. I think at least some precipitation and even a couple of severe thunderstorms are possible for about the middle of this upcoming week. More opportunities of precipitation should exist from next weekend through week 2 (~ April 9th), thanks to a somewhat southward shifted storm track due to anomalous zonal mean easterly flow across the northern high latitudes. However, it is likely the greatest precipitation amounts will be to our east and north, and southwest winds with dust storms cannot be ruled out.
I will not do another update until about Wednesday, March 29.
Ed Berry
I am not going to repeat what I just lost. SDM Stage 1 is most probable for at least the next 2 weeks, with possibly Stage 2 by week 3 should the EH tropical convective forcing (currently ~centered 0/110E with weaker thunderstorm clusters across the west Pacific) move far enough to the east (to ~150E). An active weather pattern is likely for particularly the western and central parts of the country (USA), with synoptic-scale baroclinic troughs about every 3-5 days. I have a thought of a particularly strong cyclonic development during week 2 affecting the Rockies and Plains with all relevant high-impact weather concerns (see March 23 Blog for details). In some sense, we may be seeing an enhancement of our spring-time climatology, which is not unusual for a La-Nina.
Nothing different for me to offer for southwest Kansas weather. I think at least some precipitation and even a couple of severe thunderstorms are possible for about the middle of this upcoming week. More opportunities of precipitation should exist from next weekend through week 2 (~ April 9th), thanks to a somewhat southward shifted storm track due to anomalous zonal mean easterly flow across the northern high latitudes. However, it is likely the greatest precipitation amounts will be to our east and north, and southwest winds with dust storms cannot be ruled out.
I will not do another update until about Wednesday, March 29.
Ed Berry
Thursday, March 23, 2006
I am Back
SSTs remain cooler than normal across the equatorial cold tongue with anomalies as low as ~minus 1.0C and actual temperatures ~25C. Anomalies of minus 2-3C continue to extend to depths of ~200m for the equatorial Pacific east of the date line, with comparable warmth to the west. The warm pool region remains at or slighly above normal, while positive SSTAs (weekly means) ~1-2C prevail across the subtropical regions of the South Pacific and South Indian Ocean basins (actual SSTs at least 29-30C). This spatial distribution of SSTs still projects onto a La Nina (aka a cold event). The links below provide additional information for global SSTs.
http://www.pmel.noaa.gov/tao/jsdisplay/
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
The MJO signal continues to be very weak. However, since late January, there has been roughly a 20-30 day variation of the location of the eastern hemisphere (EH) tropical convective forcing. Specifically, we have seen at least 2 episodes when the forcing oscillated between eastern Indonesia/western Pacific Ocean and the Indian Ocean regions. Time filtered hovmoller plots suggest, in addition to overall weak MJO signals, both eastward propagating convectively coupled Kelvin waves and westward moving Rossby modes have contributed to this observed behavior. The link below is an example of one of these plots.
http://www.cdc.noaa.gov/map/clim/olr_modes/hovEa.html
Additionally, monitoring tools such as animations of upper tropospheric daily mean vector wind anomalies offer some evidence that this 20-30 day tropical convective variability has been linked to extratropical baroclinic wave activity including possible jet streak induced vertical circulations. This shifting around of the tropical convective forcing has feedback into the extratropics including the PNA sector. For instance, Rossby wave energy dispersions (RWDs) linked to the convection have not only allowed anomalously deep and intense troughs to slam the USA west coast and subsequently impact the Plains with heavy precipitation and severe weather, but has also contributed to high impact weather for Hawaii.
During the past 1-2 weeks we have also observed anomalous anticyclonic wind gyres across the central north Pacific tied to the RWDs (linked to the EH tropical convection) expand into the Arctic. Zonal mean upper tropospheric easterly wind anomalies in excess of 10m/s have developed north of 60 deg. It is possible that these easterlies may contribute to the final warming of the stratosphere, which is part of the boreal spring seasonal cycle. Indicies such as the AO and NAO have become negative as a result. Also, anomalous zonal mean northern hemispheric westerly flow has shifted southward (as a response) during the past couple of weeks, from roughly 50-30N. For the CONUS this has meant a southward shift of the storm track.
SDM Stage 1 best describes the current weather-climate situation. From both the operational and reanalysis data (and their climatologies), on about March 17th tropospheric global relative atmospheric angular momentum (AAM) dipped to more than 3 standard deviations below the 1979-1998 climatology (see link below). This is the lowest value since mid January, and perhaps for even at least the past year. Large contributions to these negative anomalies are from the deep tropospheric zonal mean easterlies from both the tropical and subtropical atmospheres, as well as the Arctic (with some symmetry with the southern hemisphere).
http://www.cdc.noaa.gov/map/images/aam/glaam.gif
Per full-disk satellite imagery (see http://www.ssec.wisc.edu/data/geo/mtsat/ for example) strong tropical convection is present near the equator from ~70-100E. OLRAs are ~minus 70-90 W/m**2. This flare-up started about 5-7 days ago, and recently intensified during the past 2-3 days, as part of the tropical convective variability discussed above. I think many models will have difficulty on their predictions of especially PNA extratropics for particularly week 2 due to this convective flare-up. Secondary clusters of tropical thunderstorm activity continue over the southwest and south central Pacific Ocean due to warm SSTs. Anomalous lower tropospheric westerly flow from this convection has bred at least two tropical cyclones currently in the region Australia, as well as the recent severe cyclone Larry which impacted the northeast coast of that continent earlier this week.
SDM Stage 1 is most probable for at least the next 2 weeks. While synoptic and submonthly variations will continue (along with the circulation and SST responses due to seasonal transition), I think the tropical convective forcing and subsequent atmospheric response will remain generally stationary. This does include the anomalous northern high latitude easterlies and subsequent positive geopotential height anomalies. For the PNA sector we should continue to see the same general pattern of east Asian trough/central Pacific ridge/east Pacific into western USA trough, latter interacting with STJs due to the South Pacific convection. Because the high latitude blocking, the flow pattern across the CONUS may be split meaning a southward displaced storm track. This storm track may extend from the southwest states into the central portion of the country and then continue into the mid-Atlantic region. I think much of the USA, particularly the western 2/3rds, may become quite active again by late week 1 through week 2 (starting ~ March 29-30th).
The weather impacts to the country may include continued increased chances for much needed precipitation across the southwest USA extending into the southern and central Plains particularly week 2. I like the solutions being offered by most models of taking the system for this upcoming weekend farther north from the Pacific Northwest into the northern Plains. However, I differ with the idea of a ridge "setting up and persisting"across the western states during late week 1 and week 2 per solutions of several models (and other interpretive forecasts). One reason I feel this way is because of the above mentioned tropical convective flare-up. In reality, I think by later next week a series of more troughs may slam the west coast only to move east-northeast into the central part of the country. This would suggest more heavy precipitation for much of the western states, with severe local storms and heavy precipitation possible from the southern Plains into the Ohio Valley. Locations such as the Front Range into the Mid/Upper Mississippi Valley may still see wintery precipitation along with intense elevated thunderstorm activity. While cooler than normal for the east and opposite to that for the southwest looks good for week 1, that pattern may start to reverse week 2 (weekly mean).
For southwest Kansas, thankfully some widespread decent precipitation did occur with the last storm system. And yes, I do deserve to eat some crow (or a dead run-over road killed bull) for being persistently pessimistic. However, I do not like our precipitation chances through at least the middle of next week. We may get some "nickle and dime stuff" late this weekend and early next week. I do think there may be one or two opportunities for more beneficial precipitation roughly next weekend into the following week due to the above discussed possibly southerly displaced storm track. This may include both severe storms and snow.
Ed Berry
http://www.pmel.noaa.gov/tao/jsdisplay/
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
The MJO signal continues to be very weak. However, since late January, there has been roughly a 20-30 day variation of the location of the eastern hemisphere (EH) tropical convective forcing. Specifically, we have seen at least 2 episodes when the forcing oscillated between eastern Indonesia/western Pacific Ocean and the Indian Ocean regions. Time filtered hovmoller plots suggest, in addition to overall weak MJO signals, both eastward propagating convectively coupled Kelvin waves and westward moving Rossby modes have contributed to this observed behavior. The link below is an example of one of these plots.
http://www.cdc.noaa.gov/map/clim/olr_modes/hovEa.html
Additionally, monitoring tools such as animations of upper tropospheric daily mean vector wind anomalies offer some evidence that this 20-30 day tropical convective variability has been linked to extratropical baroclinic wave activity including possible jet streak induced vertical circulations. This shifting around of the tropical convective forcing has feedback into the extratropics including the PNA sector. For instance, Rossby wave energy dispersions (RWDs) linked to the convection have not only allowed anomalously deep and intense troughs to slam the USA west coast and subsequently impact the Plains with heavy precipitation and severe weather, but has also contributed to high impact weather for Hawaii.
During the past 1-2 weeks we have also observed anomalous anticyclonic wind gyres across the central north Pacific tied to the RWDs (linked to the EH tropical convection) expand into the Arctic. Zonal mean upper tropospheric easterly wind anomalies in excess of 10m/s have developed north of 60 deg. It is possible that these easterlies may contribute to the final warming of the stratosphere, which is part of the boreal spring seasonal cycle. Indicies such as the AO and NAO have become negative as a result. Also, anomalous zonal mean northern hemispheric westerly flow has shifted southward (as a response) during the past couple of weeks, from roughly 50-30N. For the CONUS this has meant a southward shift of the storm track.
SDM Stage 1 best describes the current weather-climate situation. From both the operational and reanalysis data (and their climatologies), on about March 17th tropospheric global relative atmospheric angular momentum (AAM) dipped to more than 3 standard deviations below the 1979-1998 climatology (see link below). This is the lowest value since mid January, and perhaps for even at least the past year. Large contributions to these negative anomalies are from the deep tropospheric zonal mean easterlies from both the tropical and subtropical atmospheres, as well as the Arctic (with some symmetry with the southern hemisphere).
http://www.cdc.noaa.gov/map/images/aam/glaam.gif
Per full-disk satellite imagery (see http://www.ssec.wisc.edu/data/geo/mtsat/ for example) strong tropical convection is present near the equator from ~70-100E. OLRAs are ~minus 70-90 W/m**2. This flare-up started about 5-7 days ago, and recently intensified during the past 2-3 days, as part of the tropical convective variability discussed above. I think many models will have difficulty on their predictions of especially PNA extratropics for particularly week 2 due to this convective flare-up. Secondary clusters of tropical thunderstorm activity continue over the southwest and south central Pacific Ocean due to warm SSTs. Anomalous lower tropospheric westerly flow from this convection has bred at least two tropical cyclones currently in the region Australia, as well as the recent severe cyclone Larry which impacted the northeast coast of that continent earlier this week.
SDM Stage 1 is most probable for at least the next 2 weeks. While synoptic and submonthly variations will continue (along with the circulation and SST responses due to seasonal transition), I think the tropical convective forcing and subsequent atmospheric response will remain generally stationary. This does include the anomalous northern high latitude easterlies and subsequent positive geopotential height anomalies. For the PNA sector we should continue to see the same general pattern of east Asian trough/central Pacific ridge/east Pacific into western USA trough, latter interacting with STJs due to the South Pacific convection. Because the high latitude blocking, the flow pattern across the CONUS may be split meaning a southward displaced storm track. This storm track may extend from the southwest states into the central portion of the country and then continue into the mid-Atlantic region. I think much of the USA, particularly the western 2/3rds, may become quite active again by late week 1 through week 2 (starting ~ March 29-30th).
The weather impacts to the country may include continued increased chances for much needed precipitation across the southwest USA extending into the southern and central Plains particularly week 2. I like the solutions being offered by most models of taking the system for this upcoming weekend farther north from the Pacific Northwest into the northern Plains. However, I differ with the idea of a ridge "setting up and persisting"across the western states during late week 1 and week 2 per solutions of several models (and other interpretive forecasts). One reason I feel this way is because of the above mentioned tropical convective flare-up. In reality, I think by later next week a series of more troughs may slam the west coast only to move east-northeast into the central part of the country. This would suggest more heavy precipitation for much of the western states, with severe local storms and heavy precipitation possible from the southern Plains into the Ohio Valley. Locations such as the Front Range into the Mid/Upper Mississippi Valley may still see wintery precipitation along with intense elevated thunderstorm activity. While cooler than normal for the east and opposite to that for the southwest looks good for week 1, that pattern may start to reverse week 2 (weekly mean).
For southwest Kansas, thankfully some widespread decent precipitation did occur with the last storm system. And yes, I do deserve to eat some crow (or a dead run-over road killed bull) for being persistently pessimistic. However, I do not like our precipitation chances through at least the middle of next week. We may get some "nickle and dime stuff" late this weekend and early next week. I do think there may be one or two opportunities for more beneficial precipitation roughly next weekend into the following week due to the above discussed possibly southerly displaced storm track. This may include both severe storms and snow.
Ed Berry
Wednesday, March 15, 2006
Short Update
Please refer to previous postings for links. Due to travel, I may not be able to write another discussion until at least a week from now (March 22), and this posting will be relatively brief.
The MJO signal is still very weak. Since my March 11 posting, tied to persistent tropical convective forcing centered on Indonesia (~0/120-140E) zonal mean anomalous easterly flow has increased throughout the tropical and subtropical atmospheres, particularly south of the equator with anomalies of ~minus 10 m/s. For the northern hemisphere (NH) zonal mean anomalous westerly flow has actually shifted south to ~30-40N with easterlies across the polar latitudes. The latter is linked to yet another anticyclonic gyre predicted by the models to retrograde from Scandanavia into Canada and Alaska during the next 2 weeks (which is reasonable). Combined with below normal sea-level pressures across major NH north-south mountain ranges (particularly east Asia), these behaviors created a large negative tendency of global relative atmospheric AAM on about March 10. Currently the global relative AAM is at least 3 standard deviations below the 1979-1998 climatology, the lowest in 2 months. A baroclinic wave packet tied to the negative AAM tendency is currently approaching the USA west coast, and will lead to closed low development across the southwestern states by this upcoming weekend.
During the last 3-5 days tropical convection has rapidly intensified across the anomalously warm waters of the equatorial IO. My thought is this region of convection may move east only to persist the Indonesian convection. The characteristics of the current circulation and tropical forcing suggest SDM Stage 4 is most representative of the weather-climate situation. SDM Stage 1 would be most probable during the next 1-2 weeks. As stated before, we are in a situation of both stationary boundary forcing and circulation response with embedded synoptic variability, taking into consideration the seasonal transition into boreal spring.
As shown by most models, the high latitude retrogression will set up a split flow pattern across the lower 48 states, leading to an anomalous ridge across central Canada and a developing storm across the southwest USA by this weekend. After some "shifting around", my thought is during week 2 the situation of strong and anomalously cold troughs hitting the west coast of North America leading to baroclinic storm development on the USA Plains will return. This all means a continuation of an active weather pattern for much of the country, suggestive of more severe storms and heavy rainfall from the southern Plains into the Ohio Valley, cold and wet for much of the west, winter precipitation and thunderstorms from the northern Plains into the Great Lakes, etc.
Southwest Kansas has some hope for precipitation this weekend, particularly Sunday into Monday. How much will depend on the track of the above discussed southwestern closed low. I am worried that as we go into week 2 (and 3) there may be 1 or 2 situations similar to what was observed on Sunday, March 11 (strong southwest (high) wind and blowing dust). It is probable most of the precipitation will again be to our east and north. However, lets see if the "seasonal cycle can help start to slow down" the recently observed fast movements of the synoptic lows from the Rockies into the Plains. After colder than normal temperatures for week 1, above normal readings are probable for week 2.
Ed Berry
The MJO signal is still very weak. Since my March 11 posting, tied to persistent tropical convective forcing centered on Indonesia (~0/120-140E) zonal mean anomalous easterly flow has increased throughout the tropical and subtropical atmospheres, particularly south of the equator with anomalies of ~minus 10 m/s. For the northern hemisphere (NH) zonal mean anomalous westerly flow has actually shifted south to ~30-40N with easterlies across the polar latitudes. The latter is linked to yet another anticyclonic gyre predicted by the models to retrograde from Scandanavia into Canada and Alaska during the next 2 weeks (which is reasonable). Combined with below normal sea-level pressures across major NH north-south mountain ranges (particularly east Asia), these behaviors created a large negative tendency of global relative atmospheric AAM on about March 10. Currently the global relative AAM is at least 3 standard deviations below the 1979-1998 climatology, the lowest in 2 months. A baroclinic wave packet tied to the negative AAM tendency is currently approaching the USA west coast, and will lead to closed low development across the southwestern states by this upcoming weekend.
During the last 3-5 days tropical convection has rapidly intensified across the anomalously warm waters of the equatorial IO. My thought is this region of convection may move east only to persist the Indonesian convection. The characteristics of the current circulation and tropical forcing suggest SDM Stage 4 is most representative of the weather-climate situation. SDM Stage 1 would be most probable during the next 1-2 weeks. As stated before, we are in a situation of both stationary boundary forcing and circulation response with embedded synoptic variability, taking into consideration the seasonal transition into boreal spring.
As shown by most models, the high latitude retrogression will set up a split flow pattern across the lower 48 states, leading to an anomalous ridge across central Canada and a developing storm across the southwest USA by this weekend. After some "shifting around", my thought is during week 2 the situation of strong and anomalously cold troughs hitting the west coast of North America leading to baroclinic storm development on the USA Plains will return. This all means a continuation of an active weather pattern for much of the country, suggestive of more severe storms and heavy rainfall from the southern Plains into the Ohio Valley, cold and wet for much of the west, winter precipitation and thunderstorms from the northern Plains into the Great Lakes, etc.
Southwest Kansas has some hope for precipitation this weekend, particularly Sunday into Monday. How much will depend on the track of the above discussed southwestern closed low. I am worried that as we go into week 2 (and 3) there may be 1 or 2 situations similar to what was observed on Sunday, March 11 (strong southwest (high) wind and blowing dust). It is probable most of the precipitation will again be to our east and north. However, lets see if the "seasonal cycle can help start to slow down" the recently observed fast movements of the synoptic lows from the Rockies into the Plains. After colder than normal temperatures for week 1, above normal readings are probable for week 2.
Ed Berry
Saturday, March 11, 2006
Same Circulation Different Day
No significant weather-climate changes since my last two postings (March 4 and8). SSTs remain ~ minus .5-2.0C below average from aboout 160E-120W along the equator and extend to depths of at least 200m. Comparable positive anomalies exist from the IO into the subtropical Pacific horshoe. This is all consistent with La-Nina, and below are links for additional details.
http://www.cdc.noaa.gov/map/clim/sst.shtml
http://www.pmel.noaa.gov/tao/jsdisplay/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
The MJO signal is virtually gone (see links below). Quasi-stationary tropical convective forcing remains quite intense centered on Indonesia ~0/140E with OLRA ~minus 50-70 w/m**2. The areal extent of these thunderstorms is from just east of the Phillipines into northern Australia. Convective flare-ups have also been occuring across South Africa and along the western portion of the SPCZ. Finally, there are weak signals that suggest convection over the IO may increase during the next few days.
http://www.cdc.noaa.gov/map/images/olr/olr.alt.anom.gif
http://www.ssec.wisc.edu/data/geo/mtsat/
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.gif
The circulation is loosely responding as would be expected. A linear combination of SDM Stages 1-2 (see http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
for the most recent version) may be representative. Trades remain above average east of the Indonesian convection while weakly anomalous surface westerly flow is still present from the east IO to north of Australia. In the upper troposphere, while zonal mean anomalous westerly flow has been propagating poleward through the subtropics of both hemispheres, anomalous zonal mean easterlies have returned to the tropical atmosphere. These easterlies have lead to a rapid decrease of global relative AAM during the past week, as seen from the link below (derived from operational data using a 1979-1998 climatology).
http://www.cdc.noaa.gov/map/images/aam/glaam.gif
This decrease of AAM, in particular the large negative tendency, is a behavior that is not quite consistent with our current situation. However, the feeling is that the atmosphere may shift back into SDM Stage 1 during the next 1-2 weeks. If interested, the link below will direct the reader to plots of the AAM budget (including the tendency) which utilize the NCEP/NCAR reanalysis data and a 1968-1997 climatology.
http://www.cdc.noaa.gov/map/clim/aam.rean.shtml
In general little change to the overall negative PNA circulation state is expected for at least the next 2 weeks (considering the seasonal cycle). Synoptic events of about every 3-5 days would be expected, with larger variations in amplitude perhaps every 10-20 days. On the latter, events such as Rossby wave energy dispersion linked to the above discussed tropical forcing (specifically the twin central Pacific subtropical cyclones, discussed in previous writings) lead to the onset of the current western CONUS trough about a week-10 days ago. A similar behavior is possible starting next weekend. Many numerical model ensemble prediction schemes are now starting to support this notion (which was not the case a few days ago).
In short, several more episodes of the same general weather that much of the country is currently getting is probable for at least the next weeks. That includes heavy precipitation for the west coast, particularly the Pacific Northwest, active winter and springtime weather on the Plains (thunderstorms and winter precipitation north/heavy rain and severe storms south) and possibly very heavy rainfall with severe storms for the Ohio and Tennessee Valleys. The coldest temperature anomalies may reside across the northern Plains and Upper Mississippi Valley with sumertime temperatures across the Deep South.
Still no respectable precipitation is in sight for southwest Kansas. In fact, while typing this Blog all I could think about was that we were having "thunderstorms in spirit" with the altostratus virga mamma cumulogenetis due to strong dynamic lifting but with little moisture. As discussed previously, we may see events like this until May. Strong surface winds leading to dust storm and fire danger hazards will be a concern until decent rounds of precipitation occur.
Ed Berry
http://www.cdc.noaa.gov/map/clim/sst.shtml
http://www.pmel.noaa.gov/tao/jsdisplay/
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
http://www.cdc.noaa.gov/people/klaus.wolter/MEI/
The MJO signal is virtually gone (see links below). Quasi-stationary tropical convective forcing remains quite intense centered on Indonesia ~0/140E with OLRA ~minus 50-70 w/m**2. The areal extent of these thunderstorms is from just east of the Phillipines into northern Australia. Convective flare-ups have also been occuring across South Africa and along the western portion of the SPCZ. Finally, there are weak signals that suggest convection over the IO may increase during the next few days.
http://www.cdc.noaa.gov/map/images/olr/olr.alt.anom.gif
http://www.ssec.wisc.edu/data/geo/mtsat/
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.gif
The circulation is loosely responding as would be expected. A linear combination of SDM Stages 1-2 (see http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
for the most recent version) may be representative. Trades remain above average east of the Indonesian convection while weakly anomalous surface westerly flow is still present from the east IO to north of Australia. In the upper troposphere, while zonal mean anomalous westerly flow has been propagating poleward through the subtropics of both hemispheres, anomalous zonal mean easterlies have returned to the tropical atmosphere. These easterlies have lead to a rapid decrease of global relative AAM during the past week, as seen from the link below (derived from operational data using a 1979-1998 climatology).
http://www.cdc.noaa.gov/map/images/aam/glaam.gif
This decrease of AAM, in particular the large negative tendency, is a behavior that is not quite consistent with our current situation. However, the feeling is that the atmosphere may shift back into SDM Stage 1 during the next 1-2 weeks. If interested, the link below will direct the reader to plots of the AAM budget (including the tendency) which utilize the NCEP/NCAR reanalysis data and a 1968-1997 climatology.
http://www.cdc.noaa.gov/map/clim/aam.rean.shtml
In general little change to the overall negative PNA circulation state is expected for at least the next 2 weeks (considering the seasonal cycle). Synoptic events of about every 3-5 days would be expected, with larger variations in amplitude perhaps every 10-20 days. On the latter, events such as Rossby wave energy dispersion linked to the above discussed tropical forcing (specifically the twin central Pacific subtropical cyclones, discussed in previous writings) lead to the onset of the current western CONUS trough about a week-10 days ago. A similar behavior is possible starting next weekend. Many numerical model ensemble prediction schemes are now starting to support this notion (which was not the case a few days ago).
In short, several more episodes of the same general weather that much of the country is currently getting is probable for at least the next weeks. That includes heavy precipitation for the west coast, particularly the Pacific Northwest, active winter and springtime weather on the Plains (thunderstorms and winter precipitation north/heavy rain and severe storms south) and possibly very heavy rainfall with severe storms for the Ohio and Tennessee Valleys. The coldest temperature anomalies may reside across the northern Plains and Upper Mississippi Valley with sumertime temperatures across the Deep South.
Still no respectable precipitation is in sight for southwest Kansas. In fact, while typing this Blog all I could think about was that we were having "thunderstorms in spirit" with the altostratus virga mamma cumulogenetis due to strong dynamic lifting but with little moisture. As discussed previously, we may see events like this until May. Strong surface winds leading to dust storm and fire danger hazards will be a concern until decent rounds of precipitation occur.
Ed Berry
Wednesday, March 08, 2006
The Atmosphere is Happy
Tropical Pacific and Indian Ocean SSTs have changed relatively little since the last Blog posting on March 4th. As shown by the following links, La-Nina conditions remain (SSTs for the Atlantic and other ocean basins can also be obtained from navigation):
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
The Atmosphere is Happy
Tropical Pacific and Indian Ocean SSTs have changed relatively little since the last Blog posting on March 4th. As shown by the following links, La-Nina conditions remain (SSTs for the Atlantic and other ocean basins can also be obtained from navigation):
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
The Atmosphere is Happy
Tropical Pacific and Indian Ocean SSTs have changed relatively little since the last Blog posting on March 4th. As shown by the following links, La-Nina conditions remain (SSTs for the Atlantic and other ocean basins can also be obtained from navigation):
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
http://www.cdc.noaa.gov/map/images/sst/sst.gif
http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif
http://www.pmel.noaa.gov/tao/jsdisplay/
Tropical convection continues over SSTs of 29C and greater, with the most intense centered on Indonesia near the equator from ~110-150E. During the past couple of days, this convection has drifted northward while extending east-southeast along the SPCZ toward the Polynesian Islands. Strong convection is also present from South Africa toward Madagascar as well as much of northern South America. Considering variations such as convectively coupled Kelvin and Rossby modes and even the diurnal cycle, the above described pattern of tropical forcing has been nearly stationary for at least the past week-10 days. The MJO signal has been very weak. As mentioned in the last posting, in terms of tropical convection, the forcing is believed to stationary and there may even be some coupling between the atmosphere and the SSTs. Stationary forcing would be probable during a La-Nina (as well as El-Nino, but with an essentially reversed distribution of tropical convection anomalies).
The circulation response is loosely consistent with what would be expected (in a composite sense) with the tropical forcing across the eastern hemisphere (EH). Interacting with synoptic variability, twin anomalous upper tropospheric subtropical anticyclones have appeared from Africa into the geographical areas of the IO and Indonesia, while twin subtropical cyclones have been present in the region of the date line. In the lower levels, while the trades have been strong east of Indonesia, actual westerlies were occuring north of Australia, all as part of a possible SST forcing atmosphere via convection positive feedback mechanism.
Linked mostly to the twin cyclones, zonal mean upper tropospheric westerly flow has been ~5-10m/s above average across the tropical and subtropical atmospheres for at least the past couple of weeks. Much of that has been in the western hemisphere (WH), including the anomalously moist STJ that has contributed to the heavy rainfall across Hawaii and the USA west coast for the past week. Recently zonal mean anomalous easterly flow has developed across subtropics particularly south of the equator, with the westerlies shifting poleward. This observation is consistent with the notion of La-Nina coupling, and AAM should be currently decreasing. In fact, the operational plot at
http://www.cdc.noaa.gov/map/images/aam/glaam.gif is supportive (uses 1979-1998 climatology verses the 1968-1997 period of the NCEP/NCAR reanalysis plots, latter which lag at least 3 days from current). Finally, also connsistent with EH tropical forcing and La-Nina, split jet stream flows have been observed across the central and eastern ccean basins of the northern extratropics. In general SDM Stages 1-2 best characterize our weather-climate situation, and it is probable that will continue for at least the next 2 weeks.
Putting into perspective for the PNA region, there has been a general east Asian trough-central Pacific ridge (with the subtropical low west of Hawaii as part of the split flow)-eastern Pacific/western USA trough pattern for at least the past week-10 days. This structure has projected onto the negative phase of the PNA teleconnection index. A Rossby wave energy dispersion (RWD) on ~March 1st, linked to the subtropical lows as part of the base state discussed above, lead to the first in a series of deep troughs for the western USA last weekend. Several more troughs are following as the parent baroclinic wave packet moves through the WH. Most models show the last in this particular series of troughs to dig deeply into the western states by the end of this upcoming weekend and then move northeast into the Plains. That is reasonable, understanding uncertainty with the details.
What I think the models have been struggling with the last few days is what happens after this weekend in terms of the circulation. From monitoring I can see that the above mentioned wave packet is rapidly coming back around into the EH subtropics. In fact, the recent blow-up of thunderstorm activity across India is being forced by the trough at the leading edge of this packet. Initially, as this subtropical wave packet interacts with the Indonesian convection (and possibly intensifies it), another RWD may occur leading to another trough digging into the east Pacific just off the USA west coast by ~ middle of next week. Similar to what has already occurred, the southern portion may break anticyclonically and re-enforce the subtropical cyclone west of Hawaii. Also from monitoring there has been~10-20 amplification periodicity forced by the east Asian topography. Trying to understand the interaction of this faster mode within the La-Nina stationary base state in anything but trivial; however, I do think ALL that may translate to more at least seasonably deep troughs for the west coast/western CONUS ~next weekend into the week of March 20th.
In my last posting I went into some length about the "weather consequences" of the above discussed reverse PNA pattern for the USA, and will not repeat here. While the west coast, particularly the Pacific Northwest gets a break from the stormy weather by early next week, at least a typical March event of baroclinic cyclogenesis is probable across the middle of the country Monday-Wednesday. In its wake, colder air will spread east and southeast from the western states across much of the country.
By next weekend into the following week, another period of active weather may return from the west coast into the Plains and Ohio Valley. Heavy precipitation would again be a concern for those areas, including severe storms from the central and southern Plains into the Ohio Valley, and winter precipitation with elevated (possibly intense) thunderstorms from the Rockies into the Upper Mississippi Valley.
Now comes the story of Southwest Kansas. Even with all the above discussed active weather, can we at least get one decent precipitation event? In my last posting I tried to be optimistic. I am afraid I will have to back off on that. Simply put, it is still too early in the year for deep layered tropical moisture to get transported this far west to interact with the intense troughs/jet streaks moving out of the Rockies. As soon as the moisture makes a run, here comes a trough, southwestly momentum is quickly transferred downward given our elevated terrain, and we mix out. In some sense this is just another rain shawdowing effect of the Rockies. As we get later into spring, at least a couple of factors become more favorable. First, deep Gulf of Mexico tropical moisture may already be in place across Texas and Oklahoma; and secondly, the magnitude of the westerly flow weakens with the seasonal cycle. So, perhaps by ~mid May and afterwards, with "this type of pattern", our precipitation chances should be much better. For now, we will leave it at that.
Other than the "nickel and dime stuff" of high-based scattered showers and storms that may occur as each trough goes by, I see little opportunity of the decent welcome precipitation that everyone wants for at least next two weeks. In fact, what may become a concern is both increased fire danger and perhaps a dust storm. Nevertheless, we need to monitor, and hopefully I will eat crow. Temperatures should trend toward below normal by early next week, only to warm to near or above by late next week.
Ed Berry
Saturday, March 04, 2006
La Nina and the Seasonal Transition into Spring
Nothing new to report in regard to the SSTs. Anomalies vary from ~minus .5-2C along the equatorial cold tongue with the coolest water around 125W having a temperature of about 24C. Anomalously cool water with readings as low as minus 5C extend to a depth of roughly 200m across the tropical east Pacific while anomalous warmth prevails at depth west of the date line. Typical of a cold event, the thermocline remains steeper than normal across the equatorial Pacific Ocean. Finally, SSTs remain above average from the South Indian Ocean (SIO) to the South Pacific (see http://www.pmel.noaa.gov/tao/jsdisplay/ and http://www.cdc.noaa.gov/map/clim/sst.shtml).
The trades remain ~5-10 m/s stronger than normal from the central into the west Pacific while comparable westerly anomalies persist from the SIO to north of Australia. The latter suggests enhanced lower tropospheric convergence around Indonesia, where intense convection has become persistent.
The MJO signal continues weak. The relatively coherent eastward movement of tropical convective forcing seen for the past few weeks has essentially stalled centered on the equator over Indonesia ~140E. Tropical thunderstorm activity remains strong from South Africa into the SIO, and there are flare-ups across the warm South Pacific SSTs. Please see the following links for details:
http://www.cdc.noaa.gov/map/clim/olr_modes/
http://www.ssec.wisc.edu/data/geo/mtsat/ (The user can navigate to other imagery)
As discussed above, the most intense tropical convective forcing is in the eastern hemisphere (EH). Over the past several months we have had nothing short of a constant interplay of tremendously complex interactions involving tropical SSTs forcing the atmosphere via convection, and the atmosphere forcing back via little understood non-linear feedbacks including those from the extratropics and even the stratosphere. Some attention to these matters has been given in previous Blogs and in our recent February 15th weather-climate discussion at http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
Additional research on understanding these issues is planned, including on extending the SDM to account for some of these behaviors.
The point of is that finally, during the past 3 weeks or so, the circulation did respond as generally would be expected with the tropical forcing shifting into the EH. At this time, anomalous twin subtropical anticylones dominate Africa and the IO with downstream twin subtropical lows around the date line. The flow is strongly split across the North Pacific with an anomalous ridge across the north central Pacific and a projection onto the negative phase of the PNA. All of this represents a circulation reversal from about early-mid February.
However, there continue to be behaviors that linear thinking will not handle. Another retrogressive high latitude anticyclonic circulation gyre is once again moving into Canada and likely headed for Alaska (which caused the NAO to be negative), and the central Pacific subtropical cyclones are displaced toward the northern hemisphere. In fact, these anomalous lows have ramped up the eastern Pacific westerly flow so much that tropospheric relative AAM is nearly 1 standard deviation above the 1968-1997 climatology (see link below).
http://www.cdc.noaa.gov/map/images/reanalysis/aam_total/glaam.sig1-21.90day.gif
For the 200mb level, this translates to at least 5-10m/s above average zonal mean westerly flow across the subtropical atmospheres of both hemispheres. Thus Stage 1 of the SDM only "loosely" represents the current-weather climate situation. In addition to feedbacks from La-Nina, the seasonal transition into boreal spring is making the atmosphere "more complicated".
In short I think we may be going into at least a quasi-persistent situation consisting of EH tropical convective forcing centered on Indonesia (near 140E) a ~SDM Stage 1-2 circulation across the PNA sector. About a year ago there was ocean-atmosphere coupling with central Pacific tropical convective forcing due to El-Nino (see http://www.cdc.noaa.gov/people/klaus.weickmann/disc022205/Draft_of_WX_CLIMATE_Disco_22FEB05.html
http://www.cdc.noaa.gov/people/klaus.weickmann/disc041505/Draft_of_WX_CLIMATE_Disco_18APR05.html for details). At that time we had SDM Stage 3, which would be expected. It is possible that a La-Nina verion of a coupling situation is now occurring. If that is the case, the lifetime is unclear. At least for week 1, the above mentioned retrogression may link up with the central Pacific ridge, leading to an even stronger projection onto a reverse PNA.
The weather for the CONUS for at least the next 7-10 days looks to be very active, with possibly several intense mobile synoptic troughs digging into the western part of the country. While most models have a reasonable handle, timing and other details are unclear after day 3 and particularly after day 5.
This means cold/wet weather is probable for much of the west coast particularly the Pacific Northwest, with an active SW-NE storm track across the Plains. While portions of the central and southern Plains may be at risk for heavy rain and severe local storms, locations from the Front Range to the Upper Mississippi Valley may be at risk for all forms of winter precipitation. Intense elevated thunderstorm activity may accompany the winter weather especially across the Upper Mississippi Valley. Finally, the Ohio and Tennessee Valley regions will also be at risk for above average rainfall and possibly severe storms. Summer-like warmth is likely for the deep south with above average temperatures for most of the east.
My suspicions is that later into week 2 (days 10-14) mobile troughs will deepen farther east toward the Rockies and Plains. That would bring colder air (there is still a source) eastward into at least the central portions of the CONUS, while the weather remains quite active. I would expect at least 1 late season winter storm across the central USA during this period.
Southwest Kansas is going to be on the storm track through at least next weekend. Most precipitation will continue to our east and north. However, there should be opportunities for at least a few rounds of showers and storms, including possibly severe. High wind, including blowing dust and fire danger, is also a concern. Opportunities for some additional precipitation should continue for week 2.
Ed Berry
The trades remain ~5-10 m/s stronger than normal from the central into the west Pacific while comparable westerly anomalies persist from the SIO to north of Australia. The latter suggests enhanced lower tropospheric convergence around Indonesia, where intense convection has become persistent.
The MJO signal continues weak. The relatively coherent eastward movement of tropical convective forcing seen for the past few weeks has essentially stalled centered on the equator over Indonesia ~140E. Tropical thunderstorm activity remains strong from South Africa into the SIO, and there are flare-ups across the warm South Pacific SSTs. Please see the following links for details:
http://www.cdc.noaa.gov/map/clim/olr_modes/
http://www.ssec.wisc.edu/data/geo/mtsat/ (The user can navigate to other imagery)
As discussed above, the most intense tropical convective forcing is in the eastern hemisphere (EH). Over the past several months we have had nothing short of a constant interplay of tremendously complex interactions involving tropical SSTs forcing the atmosphere via convection, and the atmosphere forcing back via little understood non-linear feedbacks including those from the extratropics and even the stratosphere. Some attention to these matters has been given in previous Blogs and in our recent February 15th weather-climate discussion at http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
Additional research on understanding these issues is planned, including on extending the SDM to account for some of these behaviors.
The point of is that finally, during the past 3 weeks or so, the circulation did respond as generally would be expected with the tropical forcing shifting into the EH. At this time, anomalous twin subtropical anticylones dominate Africa and the IO with downstream twin subtropical lows around the date line. The flow is strongly split across the North Pacific with an anomalous ridge across the north central Pacific and a projection onto the negative phase of the PNA. All of this represents a circulation reversal from about early-mid February.
However, there continue to be behaviors that linear thinking will not handle. Another retrogressive high latitude anticyclonic circulation gyre is once again moving into Canada and likely headed for Alaska (which caused the NAO to be negative), and the central Pacific subtropical cyclones are displaced toward the northern hemisphere. In fact, these anomalous lows have ramped up the eastern Pacific westerly flow so much that tropospheric relative AAM is nearly 1 standard deviation above the 1968-1997 climatology (see link below).
http://www.cdc.noaa.gov/map/images/reanalysis/aam_total/glaam.sig1-21.90day.gif
For the 200mb level, this translates to at least 5-10m/s above average zonal mean westerly flow across the subtropical atmospheres of both hemispheres. Thus Stage 1 of the SDM only "loosely" represents the current-weather climate situation. In addition to feedbacks from La-Nina, the seasonal transition into boreal spring is making the atmosphere "more complicated".
In short I think we may be going into at least a quasi-persistent situation consisting of EH tropical convective forcing centered on Indonesia (near 140E) a ~SDM Stage 1-2 circulation across the PNA sector. About a year ago there was ocean-atmosphere coupling with central Pacific tropical convective forcing due to El-Nino (see http://www.cdc.noaa.gov/people/klaus.weickmann/disc022205/Draft_of_WX_CLIMATE_Disco_22FEB05.html
http://www.cdc.noaa.gov/people/klaus.weickmann/disc041505/Draft_of_WX_CLIMATE_Disco_18APR05.html for details). At that time we had SDM Stage 3, which would be expected. It is possible that a La-Nina verion of a coupling situation is now occurring. If that is the case, the lifetime is unclear. At least for week 1, the above mentioned retrogression may link up with the central Pacific ridge, leading to an even stronger projection onto a reverse PNA.
The weather for the CONUS for at least the next 7-10 days looks to be very active, with possibly several intense mobile synoptic troughs digging into the western part of the country. While most models have a reasonable handle, timing and other details are unclear after day 3 and particularly after day 5.
This means cold/wet weather is probable for much of the west coast particularly the Pacific Northwest, with an active SW-NE storm track across the Plains. While portions of the central and southern Plains may be at risk for heavy rain and severe local storms, locations from the Front Range to the Upper Mississippi Valley may be at risk for all forms of winter precipitation. Intense elevated thunderstorm activity may accompany the winter weather especially across the Upper Mississippi Valley. Finally, the Ohio and Tennessee Valley regions will also be at risk for above average rainfall and possibly severe storms. Summer-like warmth is likely for the deep south with above average temperatures for most of the east.
My suspicions is that later into week 2 (days 10-14) mobile troughs will deepen farther east toward the Rockies and Plains. That would bring colder air (there is still a source) eastward into at least the central portions of the CONUS, while the weather remains quite active. I would expect at least 1 late season winter storm across the central USA during this period.
Southwest Kansas is going to be on the storm track through at least next weekend. Most precipitation will continue to our east and north. However, there should be opportunities for at least a few rounds of showers and storms, including possibly severe. High wind, including blowing dust and fire danger, is also a concern. Opportunities for some additional precipitation should continue for week 2.
Ed Berry
Wednesday, March 01, 2006
The Lion Sleeps No More
La Nina continues with SSTAs along the equatorial cold tongue varying from ~minus.5-2C, with the coolest near 120W having a temperature of around 24C. Below normal SSTs extend down to at least 200m east of the date line, with anomalies as low as -4C. From the west Pacific to the South Indian Ocean SSTs remain at least .5C above normal, with readings of at least 29c-30c, also extending down to depths of about 200m. Linked to this east to west gradient of SSTs, the trade winds have again increased during the past week with anomalies of at least 2-4 m/s.
As mentioned in the past couple of these postings, the most significant tropical convective forcing has returned into the eastern hemisphere. About a week ago a consolidation of this forcing involving a convectively coupled Rossby mode and weak MJO resulted in a flare-up near 90E along and just south of the equator. Since then a rather large area of tropical convection has been moving east fairly quickly, even projecting onto a Kelvin wave per coherent modes Hovmollers (see http://www.cdc.noaa.gov/map/clim/olr_modes/ ). Severe Hurricane Carina developed in the South Indian Ocean after the consolidation.
Per full-disk satellite imagery the above mentioned tropical thunderstorm activity covers most of Indonesia, centered around 130E. Back over the warm SSTs of the South IO, another large area of intense thunderstorm clusters have developed during the past couple of days and extend from South Africa toward Madagascar and on east. Three-day averages of OLRA of at least minus 70 w/m**2 have been observed with this activity. Finally, relatively intense convection still persists along the SPCZ due to the warm date line SSTs (see http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html). From looking a plots of OLRA, a horshoe pattern of negative anomalies can be seen fanning from the deep convection into the extratropics of both hemispheres, including the connection into Hawaii and the USA west coast.
SDM Stage 1 does capture many behaviors of the current weather-climate situation, which is typical for a cold event. Twin anomalous upper tropospheric subtropical anticyclones are becoming more robust from Africa into western Indonesia, while northward displaced twin cyclones cover the west Pacific. In fact, linked to the above mentioned tropical convective flare-up, a Rossby wave energy dispersion currently arcs from the twin cyclones across the Pacific rim linking to the trough along the North American west coast. This response does project onto the negative phase of the PNA teleconnection. Finally, split upper tropospheric flow is present across both northern hemispheric ocean basins, which includes a retrograding blocking anticyclone across the North Atlantic.
My thought is we should see the tropical convective forcing become stationary and perhaps intensify in the region of Indonesia (120-140E) for at least the next couple of weeks, given the current distribution of SSTs due to La Nina. MJO variability is likely to be weak. Flare-ups that do occur back to the west may shift east as Kelvin waves and re-enforce the stationary pattern. I would also expect the SPCZ particularly from the date line to the region of Polynesian Islands to be active from time to time. Thus it is probable the SDM Stage 1 pattern will continue during this period (into the middle of this month). With the tropical forcing residing a little farther east during the next couple of weeks than has been observed recently, I would expect troughs to dig more into the western USA than the east Pacific by week 2 (~March 8).
Now come those always unclear particularly for week 2 synoptic details for the extratropical PNA sector. With all the above and in what follows, we need to remember that the "effects" from seasonal transition into spring are also a consideration. In a probable sense, retrogression of the blocking ridge into Canada is likely by the weekend, and may link-up with the central Pacific ridge during week 2. With most models now having many of the characteristics our base state in their initial conditions, the notion portrayed of at least 1-2 anomalously deep mobile troughs digging into the western CONUS then lifting northeast into the Plains I think is a confident prediction. The storm track is likely to be depressed southward, and a moist STJ, at times, may interact with it (linked to the SPCZ).
The trough currently digging into the east Pacific should push onshore and into the Plains by the weekend, and then affect the east coast early next week. Models have a good handle on the details of that. Starting about a week from now and continuing through at least week 2, the Rockies and Plains states may be in for a very active period (the "March lion"). Initially, the Pacific Northwest states would have a concern for heavy precipitation as storms dig toward the central and southern Rockies. With possible CO/NM cyclogenesis, synoptic systems would then lift northeast into the upper Mississippi Valley/Great Lakes. Implications include heavy rain/severe local storms from the south central into the Ohio Valley states, and winter storm conditions (with possible thunderstorms) from the central/eastern Rockies into the Upper Mississippi Valley. Below normal temperatures would be expected for much of the west and northwest CONUS while the deep south may have summer-like warm and humid conditions.
For southwest Kansas, I still have to be VERY careful about raising hopes for substantial precipitation. The heaviest precipitation will clearly be to our east and north. However, I think we have the best opportunity for at least some measurable precipitation during the next couple of weeks than has been the case for at least the last 4-6 weeks. Opportunities exist for some light rainfall through about Saturday and perhaps early next week (I really hope I am being too conservative). The probability for a "wet closed low" with STJ interaction to take a favorable track just to our south is not zero for week 2. Perhaps some snowfall may result. On average, temperatures should be about normal into the middle of this month, with likely a lot of day to day variation.
Ed Berry
As mentioned in the past couple of these postings, the most significant tropical convective forcing has returned into the eastern hemisphere. About a week ago a consolidation of this forcing involving a convectively coupled Rossby mode and weak MJO resulted in a flare-up near 90E along and just south of the equator. Since then a rather large area of tropical convection has been moving east fairly quickly, even projecting onto a Kelvin wave per coherent modes Hovmollers (see http://www.cdc.noaa.gov/map/clim/olr_modes/ ). Severe Hurricane Carina developed in the South Indian Ocean after the consolidation.
Per full-disk satellite imagery the above mentioned tropical thunderstorm activity covers most of Indonesia, centered around 130E. Back over the warm SSTs of the South IO, another large area of intense thunderstorm clusters have developed during the past couple of days and extend from South Africa toward Madagascar and on east. Three-day averages of OLRA of at least minus 70 w/m**2 have been observed with this activity. Finally, relatively intense convection still persists along the SPCZ due to the warm date line SSTs (see http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html). From looking a plots of OLRA, a horshoe pattern of negative anomalies can be seen fanning from the deep convection into the extratropics of both hemispheres, including the connection into Hawaii and the USA west coast.
SDM Stage 1 does capture many behaviors of the current weather-climate situation, which is typical for a cold event. Twin anomalous upper tropospheric subtropical anticyclones are becoming more robust from Africa into western Indonesia, while northward displaced twin cyclones cover the west Pacific. In fact, linked to the above mentioned tropical convective flare-up, a Rossby wave energy dispersion currently arcs from the twin cyclones across the Pacific rim linking to the trough along the North American west coast. This response does project onto the negative phase of the PNA teleconnection. Finally, split upper tropospheric flow is present across both northern hemispheric ocean basins, which includes a retrograding blocking anticyclone across the North Atlantic.
My thought is we should see the tropical convective forcing become stationary and perhaps intensify in the region of Indonesia (120-140E) for at least the next couple of weeks, given the current distribution of SSTs due to La Nina. MJO variability is likely to be weak. Flare-ups that do occur back to the west may shift east as Kelvin waves and re-enforce the stationary pattern. I would also expect the SPCZ particularly from the date line to the region of Polynesian Islands to be active from time to time. Thus it is probable the SDM Stage 1 pattern will continue during this period (into the middle of this month). With the tropical forcing residing a little farther east during the next couple of weeks than has been observed recently, I would expect troughs to dig more into the western USA than the east Pacific by week 2 (~March 8).
Now come those always unclear particularly for week 2 synoptic details for the extratropical PNA sector. With all the above and in what follows, we need to remember that the "effects" from seasonal transition into spring are also a consideration. In a probable sense, retrogression of the blocking ridge into Canada is likely by the weekend, and may link-up with the central Pacific ridge during week 2. With most models now having many of the characteristics our base state in their initial conditions, the notion portrayed of at least 1-2 anomalously deep mobile troughs digging into the western CONUS then lifting northeast into the Plains I think is a confident prediction. The storm track is likely to be depressed southward, and a moist STJ, at times, may interact with it (linked to the SPCZ).
The trough currently digging into the east Pacific should push onshore and into the Plains by the weekend, and then affect the east coast early next week. Models have a good handle on the details of that. Starting about a week from now and continuing through at least week 2, the Rockies and Plains states may be in for a very active period (the "March lion"). Initially, the Pacific Northwest states would have a concern for heavy precipitation as storms dig toward the central and southern Rockies. With possible CO/NM cyclogenesis, synoptic systems would then lift northeast into the upper Mississippi Valley/Great Lakes. Implications include heavy rain/severe local storms from the south central into the Ohio Valley states, and winter storm conditions (with possible thunderstorms) from the central/eastern Rockies into the Upper Mississippi Valley. Below normal temperatures would be expected for much of the west and northwest CONUS while the deep south may have summer-like warm and humid conditions.
For southwest Kansas, I still have to be VERY careful about raising hopes for substantial precipitation. The heaviest precipitation will clearly be to our east and north. However, I think we have the best opportunity for at least some measurable precipitation during the next couple of weeks than has been the case for at least the last 4-6 weeks. Opportunities exist for some light rainfall through about Saturday and perhaps early next week (I really hope I am being too conservative). The probability for a "wet closed low" with STJ interaction to take a favorable track just to our south is not zero for week 2. Perhaps some snowfall may result. On average, temperatures should be about normal into the middle of this month, with likely a lot of day to day variation.
Ed Berry
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