The beat goes on today with our extended north Pacific Ocean polar jet stream and split flow/ridge conditions across the Rockies and Plains. While the west coast has received plentiful precipitation for at least the past week, wild fires have raged across the southern Plains. Will this situation persist?
Well, we have been stating (like an "old broken record") the extended Pacific basin EAJ is not consistent with where the tropical convective forcing has been (centered ~10S/120E), at least in a composite sense. However, careful monitoring suggests that various feedbacks have resulted in a "MJO-like" convective signal across the western hemisphere (WH). At the time of this posting the signal was at about 10S/60W and propagating east at around 10 m/s (~ 8 deg long/day). If this feature propagates coherently, it would reach the Indian Ocean in about 2 weeks. Thus there appears to be a "MJO-like" behavior superimposed upon our stationary eastern hemisphere (EH) tropical convective forcing. At least 2 objective tools verify this notion.
A convective signal coming back into the EH along with the on-going slow weakening of other various nonlinear physical feedback mechanisms suggests our Pacific jet should contract during the next couple of weeks. The atmospheric interactions which could allow this scenario to occur are already present, and various models have started to capture them in their initial conditions. The CDC ensemble has taken the lead, while other prediction systems such as the NCEP GFS and Canadian ensembles, and the ECMWF single run are trending (does not mean this is right).
The gist is I like the notion of ridge amplification along 120W by the middle of next week, with the possibility of discontinuous retrogression of the ridge position into the eastern Pacific after day 10. However, I have been suggesting this evolution (ridge back into east Pacific) for "one reason or another" for roughly 2 weeks, and what has occurred instead is the EAJ slamming into the west coast with storm after storm (the atmosphere is a great teacher). So, let us continue to monitor, and watch for behaviors such as more tropical convection developing across the south Indian Ocean (~60E) and merging with the persistent area farther east (~120E), the polar vortex becoming displaced toward central Asia (~90-120E) instead of the date line, and consistency with various model runs suggesting a ridge retrogression to ~140-150W.
For southwest Kansas, other than temperatures cooling toward climatology by the end of next week, no big changes. In fact, temperatures appear likely to warm again to above normal levels by next weekend into the following week. Little, if any, precipitation is in sight through at least on the order of January 10, 2006 not only for southwest Kansas, but for much of the central and southern Plains. (BIG) Maybe (with lots of uncertainty) some hopeful changes for precipitation will be seen in about 2 weeks. It will take a lot to impress me.
Ed Berry
Saturday, December 31, 2005
Throw the RED Flag
The current circulation state globally, particularly across the Asian to North American sector, has been most difficult to understand, monitor, predict and, frankly, live with, for at least the past 30 days. In spite of the most significant tropical convective forcing remaining around 120E, we have seen the polar jet stream with wind speed anomalies in excess of 30 m/s extend from, at times, north of India to the west coast of the USA.
The start of this westerly flow regime can be traced back to a Rossby wave energy dispersion linked to a western Pacific convective flare-up during early-mid November. That resulted in a blocking structure around Kamchatka. Subsequent interactions with wavetrains and the eastern hemisphere tropical convection allowed blocking at the higher latitudes to expand and, at times, cover the entire Arctic during December. While westerly flow continued to be added to the mid-latitudes from the Indian Ocean/Indonesian tropical convective forcing (and other regions, as well), dynamic feedback mechanisms from the Arctic blocking also seemingly added westerly flow to the midlatitude belt. What these feedback mechanisms were and the details of the importance and timing of individual events is unknown at this time (requires further study).
Continuing on the notion of these unclear feedbacks, there was WEAK evidence that just before Christmas a wave energy dispersion from Asia into the Pacific was forcing tropical convection across the western hemisphere, particularly in the region of the Amazon rain forest over northern South America. I then went so far to think this response may be coherent enough to propagate back into the eastern hemisphere as a "MJO like" signal (see December 31 Blog posting). Upon further review, while the idea of a weak signal coming from the extratropics into the tropics of the western hemisphere is plausible, the "MJO like" signal thinking cannot be defended for this particular case. Hence the red flag (like a NFL game!). The wave energy disturbance mentioned above has, in fact, propagated back around into the western hemisphere at this time.
With all the above stated, I do not see any real strong physical mechanism to change what is in effect SDM Stage 3 in terms of the circulation (extended north Pacific jet) at least for the next 7-10 days. There is evidence that the anomalous westerlies across the midlatitudes are shifting poleward (both hemispheres), along with increasing cyclonic flow at the polar latitudes. For the USA, this would suggest that while the Pacific northwest states gets significant precipitation, generally westerly flow with embedded disturbances should prevail across the central part of the country, much like what most models are showing, for the next 7-10 days. I refuse to go beyond day 10 since, to me, there cannot be any hope of a scientifically sound prediction in this regime.
For southwest Kansas, temperatures are likely to stay well above normal with little or no precipitation for at least the next 7-10 days (on average). A Pacific storm system may bring some sprinkles early next week. High fire danger is already a concern, and is likely to remain so at least through the end of next week.
Ed Berry
The start of this westerly flow regime can be traced back to a Rossby wave energy dispersion linked to a western Pacific convective flare-up during early-mid November. That resulted in a blocking structure around Kamchatka. Subsequent interactions with wavetrains and the eastern hemisphere tropical convection allowed blocking at the higher latitudes to expand and, at times, cover the entire Arctic during December. While westerly flow continued to be added to the mid-latitudes from the Indian Ocean/Indonesian tropical convective forcing (and other regions, as well), dynamic feedback mechanisms from the Arctic blocking also seemingly added westerly flow to the midlatitude belt. What these feedback mechanisms were and the details of the importance and timing of individual events is unknown at this time (requires further study).
Continuing on the notion of these unclear feedbacks, there was WEAK evidence that just before Christmas a wave energy dispersion from Asia into the Pacific was forcing tropical convection across the western hemisphere, particularly in the region of the Amazon rain forest over northern South America. I then went so far to think this response may be coherent enough to propagate back into the eastern hemisphere as a "MJO like" signal (see December 31 Blog posting). Upon further review, while the idea of a weak signal coming from the extratropics into the tropics of the western hemisphere is plausible, the "MJO like" signal thinking cannot be defended for this particular case. Hence the red flag (like a NFL game!). The wave energy disturbance mentioned above has, in fact, propagated back around into the western hemisphere at this time.
With all the above stated, I do not see any real strong physical mechanism to change what is in effect SDM Stage 3 in terms of the circulation (extended north Pacific jet) at least for the next 7-10 days. There is evidence that the anomalous westerlies across the midlatitudes are shifting poleward (both hemispheres), along with increasing cyclonic flow at the polar latitudes. For the USA, this would suggest that while the Pacific northwest states gets significant precipitation, generally westerly flow with embedded disturbances should prevail across the central part of the country, much like what most models are showing, for the next 7-10 days. I refuse to go beyond day 10 since, to me, there cannot be any hope of a scientifically sound prediction in this regime.
For southwest Kansas, temperatures are likely to stay well above normal with little or no precipitation for at least the next 7-10 days (on average). A Pacific storm system may bring some sprinkles early next week. High fire danger is already a concern, and is likely to remain so at least through the end of next week.
Ed Berry
Wednesday, December 28, 2005
Clear as MUD
Since my last posting, perhaps the most significant change has been the tropical convective forcing shifting into the southern hemisphere with the seasonal cycle. At this time the centroid is centered around 5-10S/110-120E, and the Australian monsoon has started. Nevertheless, in the zonal mean anomalously strong westerly flow continues across the midlatitudes of both hemispheres, with values as high as ~20 meters/sec. That includes the extended polar jet stream across the north Pacific Ocean basin, with a deep low centered around the date line and generally split flow/ridge conditions across central North America. Several weather systems will continue to impact the west coast and progress across the CONUS for at least the next 1-2 weeks (details unknown after about day 3).
As I have stated several times, the northern midlatude circulation is not consistent with the location of the tropical convective forcing. Instead, strongly nonlinear feedbacks from extratropical dynamics including the polar latitude blocks have contributed. There is evidence the nonlinear forcing is weakening with the tropics exterting an increasing influence on the global circulation.
If there is to be a linear extratropical response, then a ridge should develop across the central and eastern Pacific with a western USA trough by on the order of days 10-14 into week 3 (SDM stage 1). Indeed, many models today suggest this possibility by showing a contraction of the east Asian jet by roughly the middle of next week. However, only additional monitoring of both the weather-climate situation and model runs is the best anyone could offer in terms of days 3-14 predictions at this point. Please remember models do not predict the character of any kind of coherent tropical convective forcing beyond about days 5-7 and the details of any possible pattern change is unclear. It should go without typing that confidence in any prediction particularly across the USA (anywhere) for days 3-14 is about as low as it gets (despite what might appear to be good model agreement) at this time.
For southwest Kansas, at least through this upcoming weekend continued warmer than normal and dry. There may be an opportunity for some light precipitation in the Monday-Wednesday time frame next week (much better east and north) while temperatures stay above normal. Week 2 is unclear.
Ed Berry
As I have stated several times, the northern midlatude circulation is not consistent with the location of the tropical convective forcing. Instead, strongly nonlinear feedbacks from extratropical dynamics including the polar latitude blocks have contributed. There is evidence the nonlinear forcing is weakening with the tropics exterting an increasing influence on the global circulation.
If there is to be a linear extratropical response, then a ridge should develop across the central and eastern Pacific with a western USA trough by on the order of days 10-14 into week 3 (SDM stage 1). Indeed, many models today suggest this possibility by showing a contraction of the east Asian jet by roughly the middle of next week. However, only additional monitoring of both the weather-climate situation and model runs is the best anyone could offer in terms of days 3-14 predictions at this point. Please remember models do not predict the character of any kind of coherent tropical convective forcing beyond about days 5-7 and the details of any possible pattern change is unclear. It should go without typing that confidence in any prediction particularly across the USA (anywhere) for days 3-14 is about as low as it gets (despite what might appear to be good model agreement) at this time.
For southwest Kansas, at least through this upcoming weekend continued warmer than normal and dry. There may be an opportunity for some light precipitation in the Monday-Wednesday time frame next week (much better east and north) while temperatures stay above normal. Week 2 is unclear.
Ed Berry
Wednesday, December 21, 2005
Will the Atmosphere Synchronize at the Start of 2006?
Same old story with our weather-climate situation. Strong basin-wide extended north Pacific polar jet stream with several weather systems continues. Meanwhile, tropical convection is consolidating and intensifying around 110 east, and moving into the southern hemisphere (as part of the seasonal cycle). At the time of this writing (~0100 UTC 22 December 2005), the centroid of the large thunderstorm clusters was at about 2S/110E.
Monitoring of numerous fields in the equatorial tropics suggests that the magnitude of the stationary response to the above mentioned forcing is strengthening (yes, there is a La-Nina component to all this as suggested by the SSTs). This includes rising (falling) mean sea level pressures across the tropical eastern Pacific Ocean (Indian Ocean) with increasing surface easterlies (westerlies). Even though an infinite number of possibilities exist as to what path the atmosphere is on (including not going anywhere), "low odds" seem to favor the tropics and extratropics to "sync up" by the start of 2006. This would suggest a transition from the split flow, ridge conditions currently across western North America to more troughs particularly across the Rockies and Plains in about 10 days (around New Year's Day). We will just see what happens.
For southwest Kansas, well above normal temperatures and dry for at least the next 5-7 days can be expected. Should the changes mentioned above come to pass, colder than normal temperatures and above normal precipitation would be most probable around the first week of 2006 for much of the Plains.
Please note: I will try to do another writing at least once during about the next week. However, it may not be until the middle of next week I am able to post another discussion due to the Christmas Holiday.
Happy Holidays to everyone!
Ed Berry
Monitoring of numerous fields in the equatorial tropics suggests that the magnitude of the stationary response to the above mentioned forcing is strengthening (yes, there is a La-Nina component to all this as suggested by the SSTs). This includes rising (falling) mean sea level pressures across the tropical eastern Pacific Ocean (Indian Ocean) with increasing surface easterlies (westerlies). Even though an infinite number of possibilities exist as to what path the atmosphere is on (including not going anywhere), "low odds" seem to favor the tropics and extratropics to "sync up" by the start of 2006. This would suggest a transition from the split flow, ridge conditions currently across western North America to more troughs particularly across the Rockies and Plains in about 10 days (around New Year's Day). We will just see what happens.
For southwest Kansas, well above normal temperatures and dry for at least the next 5-7 days can be expected. Should the changes mentioned above come to pass, colder than normal temperatures and above normal precipitation would be most probable around the first week of 2006 for much of the Plains.
Please note: I will try to do another writing at least once during about the next week. However, it may not be until the middle of next week I am able to post another discussion due to the Christmas Holiday.
Happy Holidays to everyone!
Ed Berry
Monday, December 19, 2005
Ridge, "I'll be Back (Week 2?)"
Current weather-climate situation is nothing short of a "non-linear mess", and where the atmosphere is going after days 5-7 is about as unclear as it gets! While the main area of tropical convective forcing remains stationary at around 110-120E near the equator, yet another second region is at about 160E. Meanwhile, the north Pacific jet has evolved into a deep trough at roughly 150W, with 250mb wind speed anomalies on the order of 50 m/s.
We think the impacts of the seasonal cycle may be starting, with some evidence of the convection starting to move into the southern hemisphere. Will this shift reset the atmosphere like what happens when you reboot a computer? Perhaps two reasonable possibilities exist: (1) the convection suddenly shifts east (and south), and the north Pacific jet remains extended and stronger than average, or (2) forcing remains generally across the eastern hemisphere and we get more eastern Pacific/west coast anomalous ridges. While (1) is in the process of occurring for week 1 (through Christmas weekend), the scales of atmospheric balance may tilt slightly to (2) as we go into weeks 2-3 (December 26-January 9). Indeed, some of the global ensembles such as the 1200 UTC 19 Dec NCEP GFS start to rebuild the ridge strongly starting early next week. We think this situation needs to be monitored very closely.
Folks in southwest Kansas can expect dry and warmer weather through Christmas weekend. Most of the snow should melt during the next few days. From the period of December 23-26 maximum temperatures may reach well into the 60s and lower 70s. Cooler and wetter conditions may return to southwest Kansas during the first week in 2006.
We think the impacts of the seasonal cycle may be starting, with some evidence of the convection starting to move into the southern hemisphere. Will this shift reset the atmosphere like what happens when you reboot a computer? Perhaps two reasonable possibilities exist: (1) the convection suddenly shifts east (and south), and the north Pacific jet remains extended and stronger than average, or (2) forcing remains generally across the eastern hemisphere and we get more eastern Pacific/west coast anomalous ridges. While (1) is in the process of occurring for week 1 (through Christmas weekend), the scales of atmospheric balance may tilt slightly to (2) as we go into weeks 2-3 (December 26-January 9). Indeed, some of the global ensembles such as the 1200 UTC 19 Dec NCEP GFS start to rebuild the ridge strongly starting early next week. We think this situation needs to be monitored very closely.
Folks in southwest Kansas can expect dry and warmer weather through Christmas weekend. Most of the snow should melt during the next few days. From the period of December 23-26 maximum temperatures may reach well into the 60s and lower 70s. Cooler and wetter conditions may return to southwest Kansas during the first week in 2006.
Friday, December 16, 2005
It is a Watching Game
Status quo prevails. During about the past 5 days the core of the tropical convective forcing has moved east generally along/slightly north of the equator from about 120E to 140E longitude. This movement appears to be linked to the recent east Asian cold air surge and faster eastward moving coherent elements within the tropical convection. A thought is for the centroid of the convection to propagate east to around 5-10S/160E in the area of at least 30C SSTs toward the end of this month. What occurs afterwards is unclear.
I like the solution offered by most models of at least an extratropical version of SDM Stage 3 starting early next week and continuing well into week 2 (at least through Christmas weekend). This means an extended north Pacific polar jet stream with at least weakly split flow across North America (strongest westerlies across Canada). Temperature and precipitation anomalies would be expected to be above and below normal, respectively, for much of the western and northwestern USA, including southwest Kansas.
Ed Berry
I like the solution offered by most models of at least an extratropical version of SDM Stage 3 starting early next week and continuing well into week 2 (at least through Christmas weekend). This means an extended north Pacific polar jet stream with at least weakly split flow across North America (strongest westerlies across Canada). Temperature and precipitation anomalies would be expected to be above and below normal, respectively, for much of the western and northwestern USA, including southwest Kansas.
Ed Berry
Thursday, December 15, 2005
Atmospheric Tug of War
Not much new I can add to my post yesterday. However, given the cold air surge across the South China Sea, large-scale baroclinic development across the north Pacific Ocean and anomalously warm SSTs in the regions of the equatorial date line and south Pacific, I am concerned that a good portion of the tropical convective forcing may shift quickly east during the next week or so. I have been caught by these types of events before, and in this case the extratropics may now be forcing the tropics.
Nearly all global models indicate a split flow like structure across North America by late next week, with an extended jet across the north Pacific. I do go along with that, particularly if a convective signal propagates into the western hemisphere (which models initially will not capture well). We would see a SDM Stage 3 response, inspite of low global AAM.
At this point, in addition to diligent monitoring of both the models and atmosphere, we also need to pay close attention to circulation impacts due to the seasonal cycle. This includes the tropical convective forcing moving south of the equator and onset of the Australian monsoon by around the end of this month. Perhaps we will see SDM Stage 3 for much of the rest of this month followed by a transition to Stage 1 during the first 1-2 weeks in January. Interestingly it is not uncommon to see a winter storm across the Rockies and Plains during that time.
Other than a period of below normal temperatures with some light snowfall/freezing drizzle this weekend, the weather across southwest Kansas for at least the next 10 days looks generally uneventful. Temperatures should warm to above normal by late next week, and may stay that way until next year.
Nearly all global models indicate a split flow like structure across North America by late next week, with an extended jet across the north Pacific. I do go along with that, particularly if a convective signal propagates into the western hemisphere (which models initially will not capture well). We would see a SDM Stage 3 response, inspite of low global AAM.
At this point, in addition to diligent monitoring of both the models and atmosphere, we also need to pay close attention to circulation impacts due to the seasonal cycle. This includes the tropical convective forcing moving south of the equator and onset of the Australian monsoon by around the end of this month. Perhaps we will see SDM Stage 3 for much of the rest of this month followed by a transition to Stage 1 during the first 1-2 weeks in January. Interestingly it is not uncommon to see a winter storm across the Rockies and Plains during that time.
Other than a period of below normal temperatures with some light snowfall/freezing drizzle this weekend, the weather across southwest Kansas for at least the next 10 days looks generally uneventful. Temperatures should warm to above normal by late next week, and may stay that way until next year.
Wednesday, December 14, 2005
Ridge Busters on the Way???
I do think our large-scale baroclinic development event across the Pacific is going through its life-cycle, leading to the current amplification of the ridge off the North American west coast. A portion of the tropical convection has moved eastward to ~10N/160E, perhaps as a response. There is also a flare-up of thunderstorm activity around 10S/160W along the South Pacific Convergence Zone (SPCZ) due to the warm SSTs. However, the core remains centered along the equator and about 110E per satellite imagery.
Nearly all models currently suggest the north Pacific jet to outrun the convection, and impact at least the northwest USA and BC by about the middle of next week. I do think that notion is reasonable. If we do get a nice linear response to the tropical forcing, this jet should then move southward, and bring troughs into the western states by mid-late week 2 (24-28 December; go into SDM Stage 1). However, there is a tendency (seasonal cycle considerations) for these extended north Pacific jet structures to persist during winter. In fact, the single deterministic run of the ECMWF based on 1200 UTC 14 December initial conditions valid 24 December (240hrs) does show SDM Stage 3. The lobe of the polar vortex is predicted to be displaced toward the date line with split flow across North America and central Asia (and strong westerlies across the Atlantic).
If the ECMWF prediction of the circulation should verify and then persist, what gives? Again, this would not be in concert with the tropics and an overall global atmospheric circulation currently characterized by anomalously low relative atmospheric angular momentum (AAM). That is, below average westerly flow. We just need to closely monitor everything daily.
Folks is southwest Kansas can expect this upcoming weekend to colder than normal with light precipitation. By the mid to late part of next week and probably through Christmas weekend, above average temperatures with little, if any precipitation, appears most probable at this time.
Nearly all models currently suggest the north Pacific jet to outrun the convection, and impact at least the northwest USA and BC by about the middle of next week. I do think that notion is reasonable. If we do get a nice linear response to the tropical forcing, this jet should then move southward, and bring troughs into the western states by mid-late week 2 (24-28 December; go into SDM Stage 1). However, there is a tendency (seasonal cycle considerations) for these extended north Pacific jet structures to persist during winter. In fact, the single deterministic run of the ECMWF based on 1200 UTC 14 December initial conditions valid 24 December (240hrs) does show SDM Stage 3. The lobe of the polar vortex is predicted to be displaced toward the date line with split flow across North America and central Asia (and strong westerlies across the Atlantic).
If the ECMWF prediction of the circulation should verify and then persist, what gives? Again, this would not be in concert with the tropics and an overall global atmospheric circulation currently characterized by anomalously low relative atmospheric angular momentum (AAM). That is, below average westerly flow. We just need to closely monitor everything daily.
Folks is southwest Kansas can expect this upcoming weekend to colder than normal with light precipitation. By the mid to late part of next week and probably through Christmas weekend, above average temperatures with little, if any precipitation, appears most probable at this time.
Tuesday, December 13, 2005
The Wicked Ridge of the West Coast
A large area of tropical convection covers much of the eastern hemisphere from about 60-150E, generally along the equator from roughly 10S-10N. Within this envelope, two separate intense regions exist, one across the eastern Indian Ocean (IO) and the other along 140-150E. This situation of 2 areas of tropical convective forcing across the eastern hemisphere is nothing new. We have seen this behavior from time to time since about 2001, and feel that warm SST anomalies in those regions are a contributor.
Large-scale extratropical baroclinic cyclone development is currently in progress west of the date line (see satellite pictures), as evidenced by a southward surge of cold air deep into the tropics from Asia. That, along with other complex feedback issues, is allowing influences from the west Pacific convection to dominate. This means yet another jet extension and rapid amplification of the downstream ridge to a position along the North American west coast into Alaska by this weekend. Even though the models did struggle with the temporary discontinous retrogression, they did capture the above scenario very well, and we would favor the more amplified solutions such as offered by the single run of the ECMWF and CDC ensemble (all very similar). The latter includes a trough digging southward into the central Rockies this weekend. This latest ridge is not good news for west coast precipitation and the already low snow pack regions across the northwest mountains.
We feel this situation will go through a life cycle of ~10 days, and may lead to a large blocking anticyclone across Alaska by early next week. Afterwards, perhaps during the time frame of 23-30 December, the westerlies will hopefully undercut the ridge and while the IO convection becomes dominate. If that is true, this would suggest opportunites of precipitation initially over the Pacific Northwest, then spreading south, as a trough develops across the western states. Again, this is just speculation.
For the DDC CWA, initially the source for cold air is not that impressive. However, true Arctic air coming into southwest Kansas is a real possibility early next week (~ 19-21 December). Chances for decent precipitation do not look good; however, a light snowfall is a plausible concern for this weekend (similar to what we saw around 7 December).
Ed Berry
Large-scale extratropical baroclinic cyclone development is currently in progress west of the date line (see satellite pictures), as evidenced by a southward surge of cold air deep into the tropics from Asia. That, along with other complex feedback issues, is allowing influences from the west Pacific convection to dominate. This means yet another jet extension and rapid amplification of the downstream ridge to a position along the North American west coast into Alaska by this weekend. Even though the models did struggle with the temporary discontinous retrogression, they did capture the above scenario very well, and we would favor the more amplified solutions such as offered by the single run of the ECMWF and CDC ensemble (all very similar). The latter includes a trough digging southward into the central Rockies this weekend. This latest ridge is not good news for west coast precipitation and the already low snow pack regions across the northwest mountains.
We feel this situation will go through a life cycle of ~10 days, and may lead to a large blocking anticyclone across Alaska by early next week. Afterwards, perhaps during the time frame of 23-30 December, the westerlies will hopefully undercut the ridge and while the IO convection becomes dominate. If that is true, this would suggest opportunites of precipitation initially over the Pacific Northwest, then spreading south, as a trough develops across the western states. Again, this is just speculation.
For the DDC CWA, initially the source for cold air is not that impressive. However, true Arctic air coming into southwest Kansas is a real possibility early next week (~ 19-21 December). Chances for decent precipitation do not look good; however, a light snowfall is a plausible concern for this weekend (similar to what we saw around 7 December).
Ed Berry
Monday, December 12, 2005
Ridge Retrogression Underway, at Least for a Few Days
Last week we expected an event involving discontinous retrogression of the western North American ridge position, from its location along the USA/western Canadian coast this past weekend (part of a split flow structure), to around 140W. This process is occurring as I type (with the north Pacific jet being shunted northeast), and most model solutions from today such as the GFS and CDC ensembles, as well as the single ECMWF run, are now indicating this shift back into the eastern Pacific by about this coming Thursday. Downstream ramifications include baroclinic storm development across the central and northern Plains.
However, also per most model solutions, this retrogression looks to be relatively short lived. Tied to yet another east Asian cold air outbreak, I agree with the eastward movement back toward the west coast by early next week, but with large amplitude. Thus perhaps more bitterly cold arctic air can be expected to come back into much of the country by this coming weekend, along with the possibility of a second storm development across the central USA. I would expect the cold air to begin moving east early next week.
During week 2, many models again break down the PNA ridge, and have generally westerly flow across much of USA. As discussed before, that notion is not consistent dynamically with the current circulation state. We expect the tropical convective forcing to remain across the Indian Ocean and Indonesian region, suggesting the continuation (with perhaps additional reduction) of below average westerly flow globally throughout the atmosphere. A scenario that would be possible is another discontinous retrogression event on the order of days 10-14. As always, details and timing for any insights such as this are unclear. However, this would raise hopes of precipitation along the USA west coast starting days 7-10 (next week), and a welcome warm-up in temperatures over at least much of western half of the country.
For the DDC CWA, I think we need to contine minitoring the magnitude of the cold air for this upcoming weekend, as well as precipitation chances. I would expect the coldest air (relative to climo) to remain north of us, and any decent precipitation to stay to our southeast. Warmer with little chance of precipitation looks reasonable for much of next week.
Ed Berry
However, also per most model solutions, this retrogression looks to be relatively short lived. Tied to yet another east Asian cold air outbreak, I agree with the eastward movement back toward the west coast by early next week, but with large amplitude. Thus perhaps more bitterly cold arctic air can be expected to come back into much of the country by this coming weekend, along with the possibility of a second storm development across the central USA. I would expect the cold air to begin moving east early next week.
During week 2, many models again break down the PNA ridge, and have generally westerly flow across much of USA. As discussed before, that notion is not consistent dynamically with the current circulation state. We expect the tropical convective forcing to remain across the Indian Ocean and Indonesian region, suggesting the continuation (with perhaps additional reduction) of below average westerly flow globally throughout the atmosphere. A scenario that would be possible is another discontinous retrogression event on the order of days 10-14. As always, details and timing for any insights such as this are unclear. However, this would raise hopes of precipitation along the USA west coast starting days 7-10 (next week), and a welcome warm-up in temperatures over at least much of western half of the country.
For the DDC CWA, I think we need to contine minitoring the magnitude of the cold air for this upcoming weekend, as well as precipitation chances. I would expect the coldest air (relative to climo) to remain north of us, and any decent precipitation to stay to our southeast. Warmer with little chance of precipitation looks reasonable for much of next week.
Ed Berry
Saturday, December 10, 2005
Stay the Course, and Remain Alert
My previous discussions appear to be on track. Models continue to struggle. However, there is a clear trend in most solutions to finally represent the discontinuous retrogression of the North American ridge to ~30N/135W extending well into Alaska by about the middle of next week. This will favor trough and storm development across the Rockies and especially the Plains by around Tuesday-Wednesday (12/13-14). I have a concern that the baroclinic development across the central and northern Plains could be more robust than many models are showing (due to a form of low to high zonal wave number transition linked to the IO/Indonesian tropical convective forcing).
Most models continue to want to deepen a low around 150W and bring the ridge back into western North America during week 2. That is not consistent dynamically with the current weather-climate situation, and thus I do not agree with that notion. For those familiar, I think we will remain in SDM Stage 1. The second storm I discussed yesterday may, for the Plains, be slower than I offered (later during week 2). We will see.
For the DDC CWA, I may have been premature thinking yesterday we may not get any precipitation on about Tuesday (13 Dec). All things considered, including that we may get limited moisture return from the Gulf of Mexico (and there is moisture riding the STJ; see sat pics), attention needs to be paid to that matter. I do think the greatest impacts (particularly in terms of snowfall) will be to our northeast.
Most models continue to want to deepen a low around 150W and bring the ridge back into western North America during week 2. That is not consistent dynamically with the current weather-climate situation, and thus I do not agree with that notion. For those familiar, I think we will remain in SDM Stage 1. The second storm I discussed yesterday may, for the Plains, be slower than I offered (later during week 2). We will see.
For the DDC CWA, I may have been premature thinking yesterday we may not get any precipitation on about Tuesday (13 Dec). All things considered, including that we may get limited moisture return from the Gulf of Mexico (and there is moisture riding the STJ; see sat pics), attention needs to be paid to that matter. I do think the greatest impacts (particularly in terms of snowfall) will be to our northeast.
Friday, December 09, 2005
The Devil is in the Details
In essence, still on track with previous 2 postings. The anomalously intense polar jet across the western Pacific (winds in excess of 80 m/s) continues to move east, and appears the brunt of these winds will move northeast toward WA/BC during the next few days as most models suggest (along with the precipitation). The STJ should also stay in place (part of the split flow off the USA west coast), and the closed low currently along that jet west of CA should come into the southwest states by around Monday of next week.
As the retrogression of the ridge position take place early next week (linked to the tropical convective forcing across Indonesia and the Indian Ocean; this convection does not project onto a MJO), I think the notion of coupling of the northern and southern branches of the westerlies across the Rockies and Plains looks good (as also shown by most models -- now). This does suggest baroclinic storm development and another surge of cold air. I also like the solution offered by the CDC ensemble of a stronger low latitude closed low breaking through the ridge onto the CA coast by late next week, and coupling with yet another digging northern branch trough. At that point, on the order of next weekend, we may see an anomolous very large amplitude ridge from ~30N/135W extending northward well into the Arctic with more storm development across the Rockies and Plains. Later during week 2 into week 3, given the stationarity of the tropical convective forcing and other matters, yet another transient low latitude jet streak/development scenario may be probable. I think this cold regime is going to remain in place for a large part of the country for at least the next couple of weeks, with the emphasis seemingly on the central USA.
For the DDC CWA, in terms of precipitation, I suspect impacts from this first (~ Tuesday) storm will be just to our north and northeast. However, I would be concerned about the second storm being not only stronger, but farther south, for next weekend. In any event, need to monitor.
Ed Berry
As the retrogression of the ridge position take place early next week (linked to the tropical convective forcing across Indonesia and the Indian Ocean; this convection does not project onto a MJO), I think the notion of coupling of the northern and southern branches of the westerlies across the Rockies and Plains looks good (as also shown by most models -- now). This does suggest baroclinic storm development and another surge of cold air. I also like the solution offered by the CDC ensemble of a stronger low latitude closed low breaking through the ridge onto the CA coast by late next week, and coupling with yet another digging northern branch trough. At that point, on the order of next weekend, we may see an anomolous very large amplitude ridge from ~30N/135W extending northward well into the Arctic with more storm development across the Rockies and Plains. Later during week 2 into week 3, given the stationarity of the tropical convective forcing and other matters, yet another transient low latitude jet streak/development scenario may be probable. I think this cold regime is going to remain in place for a large part of the country for at least the next couple of weeks, with the emphasis seemingly on the central USA.
For the DDC CWA, in terms of precipitation, I suspect impacts from this first (~ Tuesday) storm will be just to our north and northeast. However, I would be concerned about the second storm being not only stronger, but farther south, for next weekend. In any event, need to monitor.
Ed Berry
Thursday, December 08, 2005
Models Slowly Catching On
What I posted on 8 December still looks to be on track. At this time tropical convective forcing continues to become more robust with the centroid around 5 degrees north latitude/110-120 degrees east longitude (5N/110-120E notation for future posts). There has also been fairly rapid intensification of additional thunderstorm clusters across the equatorial Indian Ocean (IO), which may help to shift the general forcing farther west during the next 1-2 weeks. Finally, partially linked to a fairly weak rapid eastward propagating convective signal across the western hemisphere, a smaller flare-up exists across warm SSTs near 10-15S/160W. Epsodic events such as the latter do contribute to subtropical jets (STJ) extending into the southwestern USA.
The extratropics continue to respond to the tropical forcing, with twin subtropical anticylones becoming established across the IO (a signal of westward shifting), in addition to those across Indonesia. This development continues to support the previous notion that the current north Pacific polar jet will break through the present east Pacific/western USA ridge by early next week (a major forecast problem for the west coast). Retrogression of the ridge position to around 140W by roughly late next week into next weekend would then be most probable, favoring a trough and possible storm development across the Rockies and Plains. Again, uncertainty continues high due to other behaviors such as nonlinear feedback issues with the current blocking present at the higher latitudes.
I have been noticing a few more models (particularly ensemble members of prediction systems such as the GFS and Canadian) catching on the above scenario the would seem more probable from weather-climate monitoring and dynamics. This tells me that as the responses due to the forcing become more robust, subsequent model initial conditions will begin to represent that.
To assist with understanding, perhaps the following link may be useful.
http://www.meteo.psu.edu/~gadomski/ewall.html
For the DDC CWA, I guess I would not expect anything "exciting" until late next week or next weekend. I will let the forecasters fill in the specifics in regard to temperature and precipitation(thanks!).
Ed Berry
The extratropics continue to respond to the tropical forcing, with twin subtropical anticylones becoming established across the IO (a signal of westward shifting), in addition to those across Indonesia. This development continues to support the previous notion that the current north Pacific polar jet will break through the present east Pacific/western USA ridge by early next week (a major forecast problem for the west coast). Retrogression of the ridge position to around 140W by roughly late next week into next weekend would then be most probable, favoring a trough and possible storm development across the Rockies and Plains. Again, uncertainty continues high due to other behaviors such as nonlinear feedback issues with the current blocking present at the higher latitudes.
I have been noticing a few more models (particularly ensemble members of prediction systems such as the GFS and Canadian) catching on the above scenario the would seem more probable from weather-climate monitoring and dynamics. This tells me that as the responses due to the forcing become more robust, subsequent model initial conditions will begin to represent that.
To assist with understanding, perhaps the following link may be useful.
http://www.meteo.psu.edu/~gadomski/ewall.html
For the DDC CWA, I guess I would not expect anything "exciting" until late next week or next weekend. I will let the forecasters fill in the specifics in regard to temperature and precipitation(thanks!).
Ed Berry
Wednesday, December 07, 2005
The Ridge Saga
This is my first posting ever on something like this. Because of time, I will have to keep these writings extremely brief. At some point we (Dr. Klaus Weickmann(PSD) and myself) hope to post more detailed weather-climate discussions weekly (at least) on the MJO experimental web site hosted by PSD at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Up to now, these have only been done as time permits. These postings do include week 1-3 outlooks primarily for the lower 48 states based on our research developing a subseasonal synoptic-dynamic model (pdf version of submitted MWR paper at http://www.cdc.noaa.gov/MJO/Predictions/ (section 8c); this paper is currently under revision for final submission).
Right now the main issue for week 1-2 predictions is how will the circulation across the Pacific-North American sector (PNA) evolve. Numerical models have struggled with problem for at least the past week, and our uncertainty continues to be very high.
Tropical convective forcing has been intensifying centered ~0/120E for the past few days, while a weaker signal has propagated into the western hemisphere. We feel that this tropical convection will remain in place for at least the next 1-2 weeks, possibly even shift slightly to the west.
Thus, the extended polar jet now across the central and western Pacific is expected to break through the current ridge during the Monday-Wednesday time frame of next week, with a subsequent discontinous retrogression to of the ridge ~140W being most probable by days 10-14. Downstream effects should include a trough developing across the Rockies, possibly extending off the California coast. This trough may interact with additional subtropical jets, and possibly lead to storm development across the Rockies and Plains during that time. In any event, monitoring is critical.
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Up to now, these have only been done as time permits. These postings do include week 1-3 outlooks primarily for the lower 48 states based on our research developing a subseasonal synoptic-dynamic model (pdf version of submitted MWR paper at http://www.cdc.noaa.gov/MJO/Predictions/ (section 8c); this paper is currently under revision for final submission).
Right now the main issue for week 1-2 predictions is how will the circulation across the Pacific-North American sector (PNA) evolve. Numerical models have struggled with problem for at least the past week, and our uncertainty continues to be very high.
Tropical convective forcing has been intensifying centered ~0/120E for the past few days, while a weaker signal has propagated into the western hemisphere. We feel that this tropical convection will remain in place for at least the next 1-2 weeks, possibly even shift slightly to the west.
Thus, the extended polar jet now across the central and western Pacific is expected to break through the current ridge during the Monday-Wednesday time frame of next week, with a subsequent discontinous retrogression to of the ridge ~140W being most probable by days 10-14. Downstream effects should include a trough developing across the Rockies, possibly extending off the California coast. This trough may interact with additional subtropical jets, and possibly lead to storm development across the Rockies and Plains during that time. In any event, monitoring is critical.
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