SSTAs remain ~minus .5-1C below normal across most of the central and eastern equatorial Pacific, from about 160E-120W. At depth, these anomalies are as low as -3C near 100m, with below normal values to at least 200m (indicative of a shallower than normal oceanic thermocline). Slightly above average SST conditions continue from the west Pacific into the subtropics east of the date line (the familiar "horse-shoe"), with values ~+2 at 150M at 165E near the equator. Typical of a cold event, there is a steeper than normal oceanic thermocline from the equatorial east Pacific into the west Pacific warm pool. See
http://www.pmel.noaa.gov/tao/jsdisplay/
for additional SST information.
As discussed previously, the divergent signal (in terms of near equatorial velocity potential) of the tropical convective forcing has been coming back around into the eastern hemisphere (EH). That can be seen from the following:
http://www.cpc.ncep.noaa.gov/products/intraseasonal/vpot_tlon.shtml
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ir_anim_monthly.shtml
Please remember that negative (positive) values mean divergence (convergence) at 200mb suggestive of upward (downward) vertical motion. Indeed, while tropical convection has weakened significantly across the western hemisphere (WH), a rapid increase has occurred across the SIO into Indonesia. In fact, what is now at least a category 1 hurricane (Carina; see link below) has developed in the central SIO. Deep moist convection also continues to "pop up" across the warm SST waters from the South Pacific back northwest into the warm pool.
http://www.npmoc.navy.mil/jtwc.html
The convection just south of the equator across the IO (~80-100E) does project onto at least a weak moist phase of the MJO. Hovmoller diagrams employing a time-filtered technique to isolate coherent convectively coupled modes support that assertion. Other statistical techniques such as the Wheeler phase diagram also lend reasonable support to defend the observation that a moist phase of the MJO has emerged in the IO (see links below).
http://www.cdc.noaa.gov/map/clim/olr_modes/
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.gif
An astute reader may want to spend some time reading on how some of these monitoring tools are derived to gain a better appreciation on interpreting them in concert with an on-going weather-climate situation. Information from these and other tools suggest to me there could be an intense convective flare-up ~120E (Indonesia) within the next couple of weeks.
The point is that the moist tropical convective forcing is now in the EH, and the circulation has responded accordingly, as defined by SDM Stage 1. For example, while zonal mean westerly anomalies have propagated into the subtropical and lower midlatitude atmospheres, easterlies are replacing them (particularly the EH). Additionally, AAM is about 1.5 standard deviations below the 1979-1998 climatology, with a contribution from the northern high latitudes in addition to the equatorial and subtropical regions. The high latitude easterlies are related to blocking activity, including the retrograding Atlantic anticyclonic gyre. Finally, we have split flow across both ocean basins with a retracted EAJ.
So, not only is the atmospheric circulation behaving as would be expected during a cold event, there is also subseasonal modulation re-enforcing it. This type of base state can cause problems with the numerical models, especially when trying to resolve the split flow patterns across the oceans. This kind of base state can/does exhibit zonal-meriodional oscillations of anomalies which are also difficult to predict beyond a few days in advance.
Most models agree on the current east Pacific trough getting kicked inland over the next few days, followed by a stronger trough later next week. There is also agreement that the Atlantic block will retrograde into Canada (not unusual for March). The latter would lead to a split flow pattern over North America (feedback from the Arctic), and depress the storm track farther south over the CONUS. This seems reasonable. After that, lots of uncertainty.
A probable option would be strongly meridional flow across CONUS by around next weekend, with perhaps closed low development across the southwest/southern Rockies. A ridge would be expected across the central and southeast states with a deep low just off the coast of the Northeast. It would then make sense to see a cyclonic storm system roll east and northeast across the rest of the country ("bowling ball") south of the ridge over Canada. Even with the high latitude ridge moving west, other similar events may follow. All of this suggests continued active periods for the west coast, welcome rainfall for parts of the southern states, and wintry precipitation for portions of the northern Plains into the Northeast.
Is there any hope for decent precipitation by around next weekend into week 2 for southwest Kansas given all the above? Short answer is to monitor. A moist STJ (along with Gulf of Mexico moisture) with a slow moving closed low going just to our south would be favorable. However, there are still too many negative factors that do not allow me to be optimistic. This upcoming week looks to be very warm (overall) and dry, with periods of strong wind. Next weekend into the following week is unclear to me in regard to precipitation. Locations from the Front Range into the Upper Mississippi Valley may get all forms of precipitation with thunderstorms, while heavy rainfall and even severe local storms would be a concern from the south central states into the Tennessee Valley.
Ed Berry
Saturday, February 25, 2006
Wednesday, February 22, 2006
Eastern Hemisphere Tropics Rule
In concert with La-Nina, SSTAs across the equatorial central and eastern Pacific remain below average, with anomalies ~minus .5-1C (SSTs ~25C) , extending to depths as low as 200m where anomalies around minus 2-3C are observed. The horshoe of anomalous warmth continues from the IO into the subtropics of the north and south Pacific, with magnitudes up to +1.5C. The warmest SSTs extend from the SIO into the South Pacific, with readings from 29-31C. It has been over these very warm waters where deep moist tropical convection has rapidly increased during the past week.
Possibly through interactions with the extratropics, there is evidence from diagnostic tools that a weak signal of the MJO has been propagating through the WH during the past 2-3 weeks (which was possibly moderate in the EH during the latter part of January), only now to re-emerge into the IO. Animations of satellite imagery clearly show the robust eruption of thunderstorm clusters over the SIO during the past week, with OLR anomalies as low as minus 90 w/m**2. Hovmollers employing a time-filtering technique to isolate coherent modes of tropical convective variability are now showing a weak projection onto the MJO. Monitoring for the next few days should give more insight into whether or not there is a decent signal of the MJO developing.
There are also intense thunderstorm clusters across the warm pool region extending southeastward along the SPCZ. Joining these 2 regions is the area of convection across Indonesia, making for a large area of forcing. How this region of enhanced precipitation will evolve during the next 1-3 weeks is unclear; however, there are some statistical and numerical tools that suggest this area to become centered ~120E by around the end of week 2. Some of these can be viewed at
http://www.cdc.noaa.gov/MJO/Forecasts/
Experience would also support that prediction.
The circulation has responded accordingly. Zonal mean upper tropospheric anomalous westerly flow is propagating into the subtropical atmosphere and being replaced by easterlies across the equatorial regions. As upper tropospheric divergence increases across the IO, twin subtropical anticyclones are developing in that region, joining with the ones already present across Africa and the Atlantic Ocean. Meanwhile, twin anomalous subtropical cyclones remain near the date line. The latter are assisting with ventilating the westerly flow out of the tropics into the subtropics, leading to the formation of STJs. One of these STJs is currently racing across the southern part of the CONUS. In short, the atmosphere appears to be transitioning from SDM Stage 4 to Stage 1. The current slow decrease of global relative tropospheric AAM from ~1 standard deviation above normal (based on a 1968-1997 climatology) to near normal adds some additional support to that notion.
As nearly all the models are now showing, for the PNA sector, initially there will be trough development just off the North American west coast (details understood) by early next week. With the moist STJ in place, substantial precipitation is a possibility again anywhere from California to Washington and eastward to the Divide late this upcoming weekend through most of next week. Downstream across the CONUS will be the Rockies ridge and eastern trough. Thus colder than normal air is likely for at least the eastern half of the country by this weekend, but not as cold as a week ago.
Another feature that is important for the weather across North America for the next 1-3 weeks is another high latitude ridge retrogression from Scandinavia into at least Canada. This kind of behavior is not unusual as we go into spring. My thought is that during the next 7-14 days the initial trough which evolves off the west coast may dig southeastward into the southern Rockies, only to eject northeast into the Plains. Models such as the GFS and Canadian ensembles give support to this option. Other troughs may follow.
The point is that the storm track should be depressed southward across the CONUS with blocking across Canada, and any ridge development over the southeast states may link up with it (as well as any central Pacific ridge). That would allow a larger amplitude flow across the country. The possibility for STJ moisture to spead northeast across the central portions would also exist, in addition to low-level moisture transport from the Gulf of Mexico and lower latitudes. So, with synoptic-scale storm development, many regions of the central and southern Plains that have been experiencing drought may get some welcome precipitation say ~March 4-10. Going along with the idea of baroclinic development, one or two significant winter storms would be a concern from the eastern Rockies into the upper Mississippi Valley with severe local storms across the south central states into perhaps the Ohio Valley.
For southwest Kansas, still dry for at least the next 7-10 days. I would like to be somewhat favorable for precipitation by the period of ~March 4-10. However, the bulk of it is likely to be to our east and north. Nevertheless, if the "more meriodional High Plains southerly flow with ejecting troughs saga" discussed above actually pans out, there is some hope for respectable preciptation. Temperatures during the next couple of weeks may average out to near normal due to rapid changes.
Ed Berry
Possibly through interactions with the extratropics, there is evidence from diagnostic tools that a weak signal of the MJO has been propagating through the WH during the past 2-3 weeks (which was possibly moderate in the EH during the latter part of January), only now to re-emerge into the IO. Animations of satellite imagery clearly show the robust eruption of thunderstorm clusters over the SIO during the past week, with OLR anomalies as low as minus 90 w/m**2. Hovmollers employing a time-filtering technique to isolate coherent modes of tropical convective variability are now showing a weak projection onto the MJO. Monitoring for the next few days should give more insight into whether or not there is a decent signal of the MJO developing.
There are also intense thunderstorm clusters across the warm pool region extending southeastward along the SPCZ. Joining these 2 regions is the area of convection across Indonesia, making for a large area of forcing. How this region of enhanced precipitation will evolve during the next 1-3 weeks is unclear; however, there are some statistical and numerical tools that suggest this area to become centered ~120E by around the end of week 2. Some of these can be viewed at
http://www.cdc.noaa.gov/MJO/Forecasts/
Experience would also support that prediction.
The circulation has responded accordingly. Zonal mean upper tropospheric anomalous westerly flow is propagating into the subtropical atmosphere and being replaced by easterlies across the equatorial regions. As upper tropospheric divergence increases across the IO, twin subtropical anticyclones are developing in that region, joining with the ones already present across Africa and the Atlantic Ocean. Meanwhile, twin anomalous subtropical cyclones remain near the date line. The latter are assisting with ventilating the westerly flow out of the tropics into the subtropics, leading to the formation of STJs. One of these STJs is currently racing across the southern part of the CONUS. In short, the atmosphere appears to be transitioning from SDM Stage 4 to Stage 1. The current slow decrease of global relative tropospheric AAM from ~1 standard deviation above normal (based on a 1968-1997 climatology) to near normal adds some additional support to that notion.
As nearly all the models are now showing, for the PNA sector, initially there will be trough development just off the North American west coast (details understood) by early next week. With the moist STJ in place, substantial precipitation is a possibility again anywhere from California to Washington and eastward to the Divide late this upcoming weekend through most of next week. Downstream across the CONUS will be the Rockies ridge and eastern trough. Thus colder than normal air is likely for at least the eastern half of the country by this weekend, but not as cold as a week ago.
Another feature that is important for the weather across North America for the next 1-3 weeks is another high latitude ridge retrogression from Scandinavia into at least Canada. This kind of behavior is not unusual as we go into spring. My thought is that during the next 7-14 days the initial trough which evolves off the west coast may dig southeastward into the southern Rockies, only to eject northeast into the Plains. Models such as the GFS and Canadian ensembles give support to this option. Other troughs may follow.
The point is that the storm track should be depressed southward across the CONUS with blocking across Canada, and any ridge development over the southeast states may link up with it (as well as any central Pacific ridge). That would allow a larger amplitude flow across the country. The possibility for STJ moisture to spead northeast across the central portions would also exist, in addition to low-level moisture transport from the Gulf of Mexico and lower latitudes. So, with synoptic-scale storm development, many regions of the central and southern Plains that have been experiencing drought may get some welcome precipitation say ~March 4-10. Going along with the idea of baroclinic development, one or two significant winter storms would be a concern from the eastern Rockies into the upper Mississippi Valley with severe local storms across the south central states into perhaps the Ohio Valley.
For southwest Kansas, still dry for at least the next 7-10 days. I would like to be somewhat favorable for precipitation by the period of ~March 4-10. However, the bulk of it is likely to be to our east and north. Nevertheless, if the "more meriodional High Plains southerly flow with ejecting troughs saga" discussed above actually pans out, there is some hope for respectable preciptation. Temperatures during the next couple of weeks may average out to near normal due to rapid changes.
Ed Berry
Eastern Hemisphere Tropics Rule
In concert with La-Nina, SSTAs across the equatorial central and eastern Pacific remain below average, with anomalies ~minus .5-1C (SSTs ~25C) , extending to depths as low as 200m where anomalies around minus 2-3C are observed. The horshoe of anomalous warmth continues from the IO into the subtropics of the north and south Pacific, with magnitudes up to +1.5C. The warmest SSTs extend from the SIO into the South Pacific, with readings from 29-31C. It has been over these very warm waters where deep moist tropical convection has rapidly increased during the past week.
Possibly through interactions with the extratropics, there is evidence from diagnostic tools that a weak signal of the MJO has been propagating through the WH during the past 2-3 weeks (which was possibly moderate in the EH during the latter part of January), only now to re-emerge into the IO. Animations of satellite imagery clearly show the robust eruption of thunderstorm clusters over the SIO during the past week, with OLR anomalies as low as minus 90 w/m**2. Hovmollers employing a time-filtering technique to isolate coherent modes of tropical convective variability are now showing a weak projection onto the MJO. Monitoring for the next few days should give more insight into whether or not there is a decent signal of the MJO developing.
There are also intense thunderstorm clusters across the warm pool region extending southeastward along the SPCZ. Joining these 2 regions is the area of convection across Indonesia, making for a large area of forcing. How this region of enhanced precipitation will evolve during the next 1-3 weeks is unclear; however, there are some statistical and numerical tools that suggest this area to become centered ~120E by around the end of week 2. Some of these can be viewed at
http://www.cdc.noaa.gov/MJO/Forecasts/
Experience would also support that prediction.
The circulation has responded accordingly. Zonal mean upper tropospheric anomalous westerly flow is propagating into the subtropical atmosphere and being replaced by easterlies across the equatorial regions. As upper tropospheric divergence increases across the IO, twin subtropical anticyclones are developing in that region, joining with the ones already present across Africa and the Atlantic Ocean. Meanwhile, twin anomalous subtropical cyclones remain near the date line. The latter are assisting with ventilating the westerly flow out of the tropics into the subtropics, leading to the formation of STJs. One of these STJs is currently racing across the southern part of the CONUS. In short, the atmosphere appears to be transitioning from SDM Stage 4 to Stage 1. The current slow decrease of global relative tropospheric AAM from ~1 standard deviation above normal (based on a 1968-1997 climatology) to near normal adds some additional support to that notion.
As nearly all the models are now showing, for the PNA sector, initially there will be trough development just off the North American west coast (details understood) by early next week. With the moist STJ in place, substantial precipitation is a possibility again anywhere from California to Washington and eastward to the Divide late this upcoming weekend through most of next week. Downstream across the CONUS will be the Rockies ridge and eastern trough. Thus colder than normal air is likely for at least the eastern half of the country by this weekend, but not as cold as a week ago.
Another feature that is important for the weather across North America for the next 1-3 weeks is another high latitude ridge retrogression from Scandinavia into at least Canada. This kind of behavior is not unusual as we go into spring. My thought is that during the next 7-14 days the initial trough which evolves off the west coast may dig southeastward into the southern Rockies, only to eject northeast into the Plains. Models such as the GFS and Canadian ensembles give support to this option. Other troughs may follow.
The point is that the storm track should be depressed southward across the CONUS with blocking across Canada, and any ridge development over the southeast states may link up with it (as well as any central Pacific ridge). That would allow a larger amplitude flow across the country. The possibility for STJ moisture to spead northeast across the central portions would also exist, in addition to low-level moisture transport from the Gulf of Mexico and lower latitudes. So, with synoptic-scale storm development, many regions of the central and southern Plains that have been experiencing drought may get some welcome precipitation say ~March 4-10. Going along with the idea of baroclinic development, one or two significant winter storms would be a concern from the eastern Rockies into the upper Mississippi Valley with severe local storms across the south central states into perhaps the Ohio Valley.
For southwest Kansas, still dry for at least the next 7-10 days. I would like to be somewhat favorable for precipitation by the period of ~March 4-10. However, the bulk of it is likely to be to our east and north. Nevertheless, if the "more meriodional High Plains southerly flow with ejecting troughs saga" discussed above actually pans out, there is some hope for respectable preciptation. Temperatures during the next couple of weeks may average out to near normal due to rapid changes.
Ed Berry
Possibly through interactions with the extratropics, there is evidence from diagnostic tools that a weak signal of the MJO has been propagating through the WH during the past 2-3 weeks (which was possibly moderate in the EH during the latter part of January), only now to re-emerge into the IO. Animations of satellite imagery clearly show the robust eruption of thunderstorm clusters over the SIO during the past week, with OLR anomalies as low as minus 90 w/m**2. Hovmollers employing a time-filtering technique to isolate coherent modes of tropical convective variability are now showing a weak projection onto the MJO. Monitoring for the next few days should give more insight into whether or not there is a decent signal of the MJO developing.
There are also intense thunderstorm clusters across the warm pool region extending southeastward along the SPCZ. Joining these 2 regions is the area of convection across Indonesia, making for a large area of forcing. How this region of enhanced precipitation will evolve during the next 1-3 weeks is unclear; however, there are some statistical and numerical tools that suggest this area to become centered ~120E by around the end of week 2. Some of these can be viewed at
http://www.cdc.noaa.gov/MJO/Forecasts/
Experience would also support that prediction.
The circulation has responded accordingly. Zonal mean upper tropospheric anomalous westerly flow is propagating into the subtropical atmosphere and being replaced by easterlies across the equatorial regions. As upper tropospheric divergence increases across the IO, twin subtropical anticyclones are developing in that region, joining with the ones already present across Africa and the Atlantic Ocean. Meanwhile, twin anomalous subtropical cyclones remain near the date line. The latter are assisting with ventilating the westerly flow out of the tropics into the subtropics, leading to the formation of STJs. One of these STJs is currently racing across the southern part of the CONUS. In short, the atmosphere appears to be transitioning from SDM Stage 4 to Stage 1. The current slow decrease of global relative tropospheric AAM from ~1 standard deviation above normal (based on a 1968-1997 climatology) to near normal adds some additional support to that notion.
As nearly all the models are now showing, for the PNA sector, initially there will be trough development just off the North American west coast (details understood) by early next week. With the moist STJ in place, substantial precipitation is a possibility again anywhere from California to Washington and eastward to the Divide late this upcoming weekend through most of next week. Downstream across the CONUS will be the Rockies ridge and eastern trough. Thus colder than normal air is likely for at least the eastern half of the country by this weekend, but not as cold as a week ago.
Another feature that is important for the weather across North America for the next 1-3 weeks is another high latitude ridge retrogression from Scandinavia into at least Canada. This kind of behavior is not unusual as we go into spring. My thought is that during the next 7-14 days the initial trough which evolves off the west coast may dig southeastward into the southern Rockies, only to eject northeast into the Plains. Models such as the GFS and Canadian ensembles give support to this option. Other troughs may follow.
The point is that the storm track should be depressed southward across the CONUS with blocking across Canada, and any ridge development over the southeast states may link up with it (as well as any central Pacific ridge). That would allow a larger amplitude flow across the country. The possibility for STJ moisture to spead northeast across the central portions would also exist, in addition to low-level moisture transport from the Gulf of Mexico and lower latitudes. So, with synoptic-scale storm development, many regions of the central and southern Plains that have been experiencing drought may get some welcome precipitation say ~March 4-10. Going along with the idea of baroclinic development, one or two significant winter storms would be a concern from the eastern Rockies into the upper Mississippi Valley with severe local storms across the south central states into perhaps the Ohio Valley.
For southwest Kansas, still dry for at least the next 7-10 days. I would like to be somewhat favorable for precipitation by the period of ~March 4-10. However, the bulk of it is likely to be to our east and north. Nevertheless, if the "more meriodional High Plains southerly flow with ejecting troughs saga" discussed above actually pans out, there is some hope for respectable preciptation. Temperatures during the next couple of weeks may average out to near normal due to rapid changes.
Ed Berry
Sunday, February 19, 2006
Back to Order in the Tropics
Just an update to previous Blog issuance on February 16. Again, please see our recent weather-climate discussion dated February 15, 2006, on the ESRL/PSD MJO web site at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
for a more in-depth look.
SST anomalies remain cooler than normal across much of the central and eastern equatorial Pacific, ~ minus .5-1C. These magnitudes have decreased during the past 7-10 days, which may be related to the seasonal cycle. Similar anomalous warmth continues from the western Pacific back into the SIO. Anomalously warm SSTs are also present across both the subtropical south and north Pacific Oceans east of the date line, somewhat flanking the cool SSTs in a "horse shoe" manner. With actual SSTs of ~25C near 140W in the equatorial cold tongue and in excess of 30C across the warm pool, the trades have been slowly re-strengthening. Low-level easterlies have also been increasing across the SIO during the past week.
The MJO is very weak. Tropical convective forcing has significantly re-emerged across the eastern hemisphere (EH) during the past week, currently centered ~5-10S/140E. Intense thunderstorm activity extends westward well into the SIO and to the east along the SPCZ to 140W. The latter is a response to the warm SSTs in that region. What MJO signal that remains from a few weeks ago is believed to be contributing to this EH intensification.
All of the above is consistent with expected behaviors from the tropics during a cold event. The extratropics are also responding accordingly. The EAJ has retracted, with poleward displaced twin anticyclones near 140E and downstream twin subtropical cyclones now around the date line (leading to a STJ into the southern CONUS). A trough-ridge-trough pattern extends from Asia-North America, projecting onto the negative (or reverse phase) of the PNA (a.k.a. RNA when negative), with split flow across the central and eastern Pacific. Split flow is also becoming present across the Atlantic. Finally, with zonal mean easterly anomalies over the high and subtropical latitudes and still westerly anomalies near the equator and midlatitudes for both hemispheres, relative tropospheric AAM is decreasing. Tools such as time-latitude sections of zonal mean zonal wind anomalies do give a signal of the westerly anomalies starting to move off the equator into the subtropics, with easterlies replacing them.
Similar to what was observed about a month ago, I would expect the most significant lobe of the polar vortex to become re-established across central and eastern Asia. It would not be unreasonable to see a trough dig into the east Pacific in about a week, as the extratropics continue to respond to the re-intensification of the EH forcing. That is also similar to what happened nearly a month ago. As most models show, that would lead to a transient synoptic ridge amplification along the west coast and allow a trough to deepen across the central and eastern states. A surge of Arctic air would accompany this trough.
I would think with the zonal mean westerly anomalies coming off the equator the EAJ would extend in roughly 7-14 days. This would result in a downstream progression of synoptic features, in the overall "RNA/Pacific (and Atlantic) split flow pattern" discussed above. As the CDC ensemble shows for week 2, a deep trough would be probable for the Pacific Northwest and northern Rockies with ridging across the south central and south east states. The storm track would likely be from the from the west coast into the Northern Plains. In general, by week 2 (2/27-3/5) in terms of the circulation SDM Stage 1 would be most probable (currently Stage 4 with the STJs).
Week 1 impacts would include another surge of an Arctic airmass into much of the central and eastern states, but not as cold as its predecessor. The wettest locations should include some precipitation for the Pacific Northwest as well as the southeastern states. By week 2 locations from roughly northern California in the Pacific Northwest may see significant precipitation. Those locations would also be expected to remain cooler than normal. Colder than normal weather may also linger across the northeast states as blocking develops across the North Atlantic during week 1. Similar to a recent high latitude retrogression (see past postings), that North Atlantic block may shift west into northern Canada during week 2. Finally, warm and dry conditions are probable for the central and southern Plains into the southeast. The northern Plains may also become active with possibly 1-2 events of baroclinic cyclogenesis.
Nothing new for southwest Kansas. Still looks like little or no precipitation for the next 2 weeks. Temperatures should warm this upcoming week to above normal, followed by cooler than normal temperatures for about next weekend. Above normal temperatures are then probable for the following week going into the first part of March.
Ed Berry
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
for a more in-depth look.
SST anomalies remain cooler than normal across much of the central and eastern equatorial Pacific, ~ minus .5-1C. These magnitudes have decreased during the past 7-10 days, which may be related to the seasonal cycle. Similar anomalous warmth continues from the western Pacific back into the SIO. Anomalously warm SSTs are also present across both the subtropical south and north Pacific Oceans east of the date line, somewhat flanking the cool SSTs in a "horse shoe" manner. With actual SSTs of ~25C near 140W in the equatorial cold tongue and in excess of 30C across the warm pool, the trades have been slowly re-strengthening. Low-level easterlies have also been increasing across the SIO during the past week.
The MJO is very weak. Tropical convective forcing has significantly re-emerged across the eastern hemisphere (EH) during the past week, currently centered ~5-10S/140E. Intense thunderstorm activity extends westward well into the SIO and to the east along the SPCZ to 140W. The latter is a response to the warm SSTs in that region. What MJO signal that remains from a few weeks ago is believed to be contributing to this EH intensification.
All of the above is consistent with expected behaviors from the tropics during a cold event. The extratropics are also responding accordingly. The EAJ has retracted, with poleward displaced twin anticyclones near 140E and downstream twin subtropical cyclones now around the date line (leading to a STJ into the southern CONUS). A trough-ridge-trough pattern extends from Asia-North America, projecting onto the negative (or reverse phase) of the PNA (a.k.a. RNA when negative), with split flow across the central and eastern Pacific. Split flow is also becoming present across the Atlantic. Finally, with zonal mean easterly anomalies over the high and subtropical latitudes and still westerly anomalies near the equator and midlatitudes for both hemispheres, relative tropospheric AAM is decreasing. Tools such as time-latitude sections of zonal mean zonal wind anomalies do give a signal of the westerly anomalies starting to move off the equator into the subtropics, with easterlies replacing them.
Similar to what was observed about a month ago, I would expect the most significant lobe of the polar vortex to become re-established across central and eastern Asia. It would not be unreasonable to see a trough dig into the east Pacific in about a week, as the extratropics continue to respond to the re-intensification of the EH forcing. That is also similar to what happened nearly a month ago. As most models show, that would lead to a transient synoptic ridge amplification along the west coast and allow a trough to deepen across the central and eastern states. A surge of Arctic air would accompany this trough.
I would think with the zonal mean westerly anomalies coming off the equator the EAJ would extend in roughly 7-14 days. This would result in a downstream progression of synoptic features, in the overall "RNA/Pacific (and Atlantic) split flow pattern" discussed above. As the CDC ensemble shows for week 2, a deep trough would be probable for the Pacific Northwest and northern Rockies with ridging across the south central and south east states. The storm track would likely be from the from the west coast into the Northern Plains. In general, by week 2 (2/27-3/5) in terms of the circulation SDM Stage 1 would be most probable (currently Stage 4 with the STJs).
Week 1 impacts would include another surge of an Arctic airmass into much of the central and eastern states, but not as cold as its predecessor. The wettest locations should include some precipitation for the Pacific Northwest as well as the southeastern states. By week 2 locations from roughly northern California in the Pacific Northwest may see significant precipitation. Those locations would also be expected to remain cooler than normal. Colder than normal weather may also linger across the northeast states as blocking develops across the North Atlantic during week 1. Similar to a recent high latitude retrogression (see past postings), that North Atlantic block may shift west into northern Canada during week 2. Finally, warm and dry conditions are probable for the central and southern Plains into the southeast. The northern Plains may also become active with possibly 1-2 events of baroclinic cyclogenesis.
Nothing new for southwest Kansas. Still looks like little or no precipitation for the next 2 weeks. Temperatures should warm this upcoming week to above normal, followed by cooler than normal temperatures for about next weekend. Above normal temperatures are then probable for the following week going into the first part of March.
Ed Berry
Thursday, February 16, 2006
Baby Girl Wakes Up Old Man Winter
First, the URL for the recent weather-climate discussion Klaus and I posted (dated February 15,2006) is
http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
All of our postings can be found at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
In our recent report a review of the circulation anomalies and tropical convective forcing since late last fall was given. We also give an overview for about the past year documenting a transition from El-Nino to La-Nina. With all of that, perhaps I will be able to keep this Blog posting a bit shorter (no luck!).
Central and eastern Pacific SSTs continue about .5-1.0C below normal from ~160E-120W, and extend to depths of about 250-300m, with values as low as minus 3C. In contrast, SSTAs of +.5-1.0C continue over the west Pacific, with anomalies of ~ +2C at near 100m/160E along the equator. Actual SSTs along the equatorial cold tongue are as low as 25C while still in excess of 30C across portions of the west Pacific warm pool. The recent moderation of the cool equatorial SSTs, with even slightly warmer than average west of South America, may be related to the seasonal cycle and recent MJO activity. In any case, there continues to be an enhanced east-west gradient of SSTs maintaining the cold event conditions, including a resumption of enhanced surface easterlies from the tropical west Pacific into the South Indian Ocean (SIO).
The MJO is weak. Monitoring suggests a diffuse signal is currently re-emerging into the eastern hemisphere. Satellite imagery indicates that while a slow weakening of thunderstorm activity across the Amazon Rainforest and Brasil has been occurring, a slow increase has been in progress across the SIO, all during the past week (in an area that has seen very strong suppression for at least 2 weeks). Fairly warm SSTs across the SIO should continue that trend for more convection. Additional thunderstorm activity has also been on the increase across Indonesia (partly due to a westward shift from the SPCZ), and may be starting to interact with the convection farther west. Experience suggests the tropical forcing to become robust ~100-120E within the next 7-14 days, and there are statistical tools to support that notion. This pattern of east IO enhancement with central equatorial Pacific suppression would be consistent with La-Nina. Also consistent would periodic enhancement along the SPCZ, and above average SSTs in that region would support it.
Animations of northern extratropical circulation anomalies suggest the recent retrogression is linking up with the increasing eastern hemisphere tropical forcing. That is, northward displaced upper tropospheric twin anticyclones (with downstream twin cyclones) have phased nicely with a Rossby wave train across the north Pacific leading to our current negative phase of the PNA (western USA trough). In the context of the SDM, a transition from Stage 4-1 of the circulation may be in progress. Once established, SDM Stage 1 may persist at least into early March.
With the developing pattern of tropical convective forcing expected to persist for at least the next couple of weeks, so should the reverse PNA. Most models are in general agreement for this scenario; it is just a matter of monitoring amplitude variations. On going research work and synoptic experience suggests there may be zonal to meridional vacillations within this quasi-stationary pattern of a ~150W ridge and 120W trough. That could include anticyclonic wave breaking events of lows just off the Pacific Northwest coast, and possibly farther south.
In short, tropical forcing consistent with La-Nina has allowed an extratropical response across the PNA sector that would be expected from a cold event. So far the result has been a resurrection of winter for much of the north and west CONUS, including the coldest temperatures so far this winter. An active storm track across the central part of the country has also materialized. There should be at least one more storm along this track during the next 5-7 days, except a bit farther south than the current one (2/16), and the east Pacific STJ will likely contribute to it.
Should the convection become very intense in the region of Indonesia, an amplification of the central Pacific ridge may lead to an intense cyclonic storm over or just offshore from the Pacific Northwest by week 2. That system may then propagate downstream and maintain an active storm track from the Pacific Northwest into the Plains. While temperatures remain below normal across the north and west, above normal readings may occur across the southeast.
For southwest Kansas, I wish I could offer more optimism about precipitation. The second storm mentioned above gives some hope for light amounts on about Sunday. That may be in the form of freezing drizzle in addition to any light snow. After that, with the storm track staying to our north and systems remaining progressive, unfortunately little or no precipitation for at least the next 2 weeks. I hope this is wrong. Well below normal temperatures will continue through at least early next week, then moderate to at least about normal through week 2.
Ed Berry
http://www.cdc.noaa.gov/people/klaus.weickmann/disc021506/weather_climate_discussion_10Feb06.html
All of our postings can be found at
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
In our recent report a review of the circulation anomalies and tropical convective forcing since late last fall was given. We also give an overview for about the past year documenting a transition from El-Nino to La-Nina. With all of that, perhaps I will be able to keep this Blog posting a bit shorter (no luck!).
Central and eastern Pacific SSTs continue about .5-1.0C below normal from ~160E-120W, and extend to depths of about 250-300m, with values as low as minus 3C. In contrast, SSTAs of +.5-1.0C continue over the west Pacific, with anomalies of ~ +2C at near 100m/160E along the equator. Actual SSTs along the equatorial cold tongue are as low as 25C while still in excess of 30C across portions of the west Pacific warm pool. The recent moderation of the cool equatorial SSTs, with even slightly warmer than average west of South America, may be related to the seasonal cycle and recent MJO activity. In any case, there continues to be an enhanced east-west gradient of SSTs maintaining the cold event conditions, including a resumption of enhanced surface easterlies from the tropical west Pacific into the South Indian Ocean (SIO).
The MJO is weak. Monitoring suggests a diffuse signal is currently re-emerging into the eastern hemisphere. Satellite imagery indicates that while a slow weakening of thunderstorm activity across the Amazon Rainforest and Brasil has been occurring, a slow increase has been in progress across the SIO, all during the past week (in an area that has seen very strong suppression for at least 2 weeks). Fairly warm SSTs across the SIO should continue that trend for more convection. Additional thunderstorm activity has also been on the increase across Indonesia (partly due to a westward shift from the SPCZ), and may be starting to interact with the convection farther west. Experience suggests the tropical forcing to become robust ~100-120E within the next 7-14 days, and there are statistical tools to support that notion. This pattern of east IO enhancement with central equatorial Pacific suppression would be consistent with La-Nina. Also consistent would periodic enhancement along the SPCZ, and above average SSTs in that region would support it.
Animations of northern extratropical circulation anomalies suggest the recent retrogression is linking up with the increasing eastern hemisphere tropical forcing. That is, northward displaced upper tropospheric twin anticyclones (with downstream twin cyclones) have phased nicely with a Rossby wave train across the north Pacific leading to our current negative phase of the PNA (western USA trough). In the context of the SDM, a transition from Stage 4-1 of the circulation may be in progress. Once established, SDM Stage 1 may persist at least into early March.
With the developing pattern of tropical convective forcing expected to persist for at least the next couple of weeks, so should the reverse PNA. Most models are in general agreement for this scenario; it is just a matter of monitoring amplitude variations. On going research work and synoptic experience suggests there may be zonal to meridional vacillations within this quasi-stationary pattern of a ~150W ridge and 120W trough. That could include anticyclonic wave breaking events of lows just off the Pacific Northwest coast, and possibly farther south.
In short, tropical forcing consistent with La-Nina has allowed an extratropical response across the PNA sector that would be expected from a cold event. So far the result has been a resurrection of winter for much of the north and west CONUS, including the coldest temperatures so far this winter. An active storm track across the central part of the country has also materialized. There should be at least one more storm along this track during the next 5-7 days, except a bit farther south than the current one (2/16), and the east Pacific STJ will likely contribute to it.
Should the convection become very intense in the region of Indonesia, an amplification of the central Pacific ridge may lead to an intense cyclonic storm over or just offshore from the Pacific Northwest by week 2. That system may then propagate downstream and maintain an active storm track from the Pacific Northwest into the Plains. While temperatures remain below normal across the north and west, above normal readings may occur across the southeast.
For southwest Kansas, I wish I could offer more optimism about precipitation. The second storm mentioned above gives some hope for light amounts on about Sunday. That may be in the form of freezing drizzle in addition to any light snow. After that, with the storm track staying to our north and systems remaining progressive, unfortunately little or no precipitation for at least the next 2 weeks. I hope this is wrong. Well below normal temperatures will continue through at least early next week, then moderate to at least about normal through week 2.
Ed Berry
Saturday, February 11, 2006
Moving Waves
First, we are still in the process of working on a weather-climate discussion for the PSD MJO web page. A draft has been written, and we hope to post the final version next week. The link is:
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
La-Nina continues, with subnormal SSTs along the central and eastern equatorial Pacific extending to depths of at least 250m. Recent 5-day averaged surface anomalies are ~minus 1.5C near 160W, with actual SSTs near 25C. The coolest anomalies have been moving westward along the equatorial cold tongue. Above average tropical Pacific SSTs are confined near 10S/160E, with actual temperatures ~30C. We are approaching the time of year when, for the cold tongue region, actual SSTs are warmest, climatologically March and April. This may impact the anomalies in the coming weeks.
For SST information, please see:
http://www.pmel.noaa.gov/tao/jsdisplay/
Please see the latest CPC ENSO advisory for additional information on the current cold event:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
A weak to moderate MJO was in progress from about mid January into the first few days of this month. This event initiated north of Australia, and resulted in very intense convection along the SPCZ by late January. Although much weaker, the signal has moved into the western hemisphere (WH). This can be observed on satellite imagery by noting the enhanced thunderstorm activity across northern South America (Amazon Rainforest and southeast Brasil) and South Africa. The intensity of the SPCZ convection has weakened, with the most intense core back to ~0/140E. During the next couple of weeks a probable scenario would be for the convection with the MJO signal to consolidate with the area north of Australia. The result may be an intense region of forcing from ~100-140E similar to the first half of January, and this would be consistent with La-Nina.
The extratropics have also continued to do their own thing with the wave 0-2 (to keep things simple) retrogressive transient that has been going on (likely linked to a recent major sudden stratospheric warming). With the most significant lobe of the polar vortex displaced toward east Asia, a zonal wave number 3 pattern of troughs and ridges has evolved. Troughs are present across Eastern Asia and North America, and Europe. This has lead to a strong positive phase of the PNA (for now).
As the tropical forcing intensifies around Indonesia during the next couple of weeks, I would think the final stages of this retrogression should "lock in". Consistent with La-Nina in a composite sense, and just as the models show, a central Pacific ridge and western North American trough would be expected. This would project onto a negative phase of the PNA. While blocking across Alaska and cold regime for particularly the western and central USA seems likely per models including the CDC ensemble, amplitude details are uncertain especially for the western North American trough.
There are also other sources of uncertainty from, for instance, the future course of the above average zonal mean westerly flow across the equatorial and subtropical atmospheres (anomalies ~5-10 m/s) and the easterly flow on the poleward flanks. I would expect this westerly flow to at least locally propagate into the midlatitudes via subtropical jets (STJs, which are already present), and be replaced by deep zonal mean easterly thoughout the tropics and subtropics during the next few weeks. This would decrease the globally averaged AAM, also consistent with La-Nina.
In terms of the SDM, we are currently going into Stage 4, with a transition to Stage 1 most probable by the end of week 2 into week 3. For the PNA sector, this would translate to a northward shifted storm track with time.
When making week1-3 predictions of any kind, the above is only a small subset of the considerations attention must be paid. These are just a few of the sources of sensitivities for numerical models, and is why you will see run-run inconsistencies, model differences, etc., especially in a regime such as this.
I think much of the CONUS is in for a relatively cold regime week 1 (variations understood), perhaps shifting more into the Pacific Northwest, northern and central Rockies and Plains week 2. There already is evidence of cross-polar flow of Arctic air from Asia, and this will likely come into the western USA this week. During week 2-3 it is possible the southeastern states will warm to above normal temperatures.
With the trough developing across the western USA, an active pattern is probable for much of the country for the next 2-3 weeks. The focus may be the Plains. However, we will need to watch how far along or off the west coast one or 2 synoptic-scale troughs may initially dig. I do think there may be 1-2 cold/wet episodes for the west coast during roughly the next 10 days. That could include snow for locations such as Seattle. Afterwards, mainly the Pacific Northwest may be impacted. For the Plains, while significant winter weather occurs across the north, locations such as the Ohio Valley may see a lot of rain/thunderstorms (with icing in-between).
Now comes southwest Kansas. Even with all the above, I am not at all optimistic about significant precipitation for at least the next 2-3 weeks. The heaviest will easily be to our north and east. In this type of pattern, low pressure systems are going to tend to be progressive, with our location favored for the dry slots. The notion of shallow Arctic cold air with a few hundredths liquid (perhaps) of freezing drizzle/snow has some merit by the end of this upcoming week into the weekend. However, I cannot rule out a STJ system bringing some precipitation anytime. I hope the atmosphere surprises me, and I am wrong about our precipitation chances. After a warm start, temperatures should lower to below normal the end of the week.
Ed Berry
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
La-Nina continues, with subnormal SSTs along the central and eastern equatorial Pacific extending to depths of at least 250m. Recent 5-day averaged surface anomalies are ~minus 1.5C near 160W, with actual SSTs near 25C. The coolest anomalies have been moving westward along the equatorial cold tongue. Above average tropical Pacific SSTs are confined near 10S/160E, with actual temperatures ~30C. We are approaching the time of year when, for the cold tongue region, actual SSTs are warmest, climatologically March and April. This may impact the anomalies in the coming weeks.
For SST information, please see:
http://www.pmel.noaa.gov/tao/jsdisplay/
Please see the latest CPC ENSO advisory for additional information on the current cold event:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.html
A weak to moderate MJO was in progress from about mid January into the first few days of this month. This event initiated north of Australia, and resulted in very intense convection along the SPCZ by late January. Although much weaker, the signal has moved into the western hemisphere (WH). This can be observed on satellite imagery by noting the enhanced thunderstorm activity across northern South America (Amazon Rainforest and southeast Brasil) and South Africa. The intensity of the SPCZ convection has weakened, with the most intense core back to ~0/140E. During the next couple of weeks a probable scenario would be for the convection with the MJO signal to consolidate with the area north of Australia. The result may be an intense region of forcing from ~100-140E similar to the first half of January, and this would be consistent with La-Nina.
The extratropics have also continued to do their own thing with the wave 0-2 (to keep things simple) retrogressive transient that has been going on (likely linked to a recent major sudden stratospheric warming). With the most significant lobe of the polar vortex displaced toward east Asia, a zonal wave number 3 pattern of troughs and ridges has evolved. Troughs are present across Eastern Asia and North America, and Europe. This has lead to a strong positive phase of the PNA (for now).
As the tropical forcing intensifies around Indonesia during the next couple of weeks, I would think the final stages of this retrogression should "lock in". Consistent with La-Nina in a composite sense, and just as the models show, a central Pacific ridge and western North American trough would be expected. This would project onto a negative phase of the PNA. While blocking across Alaska and cold regime for particularly the western and central USA seems likely per models including the CDC ensemble, amplitude details are uncertain especially for the western North American trough.
There are also other sources of uncertainty from, for instance, the future course of the above average zonal mean westerly flow across the equatorial and subtropical atmospheres (anomalies ~5-10 m/s) and the easterly flow on the poleward flanks. I would expect this westerly flow to at least locally propagate into the midlatitudes via subtropical jets (STJs, which are already present), and be replaced by deep zonal mean easterly thoughout the tropics and subtropics during the next few weeks. This would decrease the globally averaged AAM, also consistent with La-Nina.
In terms of the SDM, we are currently going into Stage 4, with a transition to Stage 1 most probable by the end of week 2 into week 3. For the PNA sector, this would translate to a northward shifted storm track with time.
When making week1-3 predictions of any kind, the above is only a small subset of the considerations attention must be paid. These are just a few of the sources of sensitivities for numerical models, and is why you will see run-run inconsistencies, model differences, etc., especially in a regime such as this.
I think much of the CONUS is in for a relatively cold regime week 1 (variations understood), perhaps shifting more into the Pacific Northwest, northern and central Rockies and Plains week 2. There already is evidence of cross-polar flow of Arctic air from Asia, and this will likely come into the western USA this week. During week 2-3 it is possible the southeastern states will warm to above normal temperatures.
With the trough developing across the western USA, an active pattern is probable for much of the country for the next 2-3 weeks. The focus may be the Plains. However, we will need to watch how far along or off the west coast one or 2 synoptic-scale troughs may initially dig. I do think there may be 1-2 cold/wet episodes for the west coast during roughly the next 10 days. That could include snow for locations such as Seattle. Afterwards, mainly the Pacific Northwest may be impacted. For the Plains, while significant winter weather occurs across the north, locations such as the Ohio Valley may see a lot of rain/thunderstorms (with icing in-between).
Now comes southwest Kansas. Even with all the above, I am not at all optimistic about significant precipitation for at least the next 2-3 weeks. The heaviest will easily be to our north and east. In this type of pattern, low pressure systems are going to tend to be progressive, with our location favored for the dry slots. The notion of shallow Arctic cold air with a few hundredths liquid (perhaps) of freezing drizzle/snow has some merit by the end of this upcoming week into the weekend. However, I cannot rule out a STJ system bringing some precipitation anytime. I hope the atmosphere surprises me, and I am wrong about our precipitation chances. After a warm start, temperatures should lower to below normal the end of the week.
Ed Berry
Monday, February 06, 2006
The Atmosphere is Going into Reverse
Since we are working this week on a long overdue posting of a weather-climate discussion for the ESRL/PSD (formally CDC) MJO web site, this will be the last writing on this Blog until at least this Friday (2/10). The link to these discussions is
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Slow but important changes are occurring across both the tropics and extratropics. SST anomalies remain below normal across the equatorial central and eastern Pacific, with values at least as cold as -2C and actual SSTs around 24C centered on 145W. Ocean surface temperatures remain slightly above average across the south and west Pacific, with anomalies ~ +.5-1C and SSTs from 29-31C centered near 10-15S/160E. This pattern is reflective of La-Nina.
After 4 months of little MJO variability, during the past couple of weeks or so there has been a coherent but relatively weak signal of the MJO propagating east from just north of Australia to roughly the southern eastern Pacific. One response from this MJO was very intense convection along the South Pacific Convergence Zone (SPCZ) over the warm SSTs this past week. The SPCZ convection added anomalous westerly flow to the tropical and subtropical atmosphere. In addition, feedbacks from the polar latitudes including the wave number 1 retrogressive transient (discussed in previous postings) added anomalous westerly flow to the northern extratropics (with similar behaviors perhaps across the southern hemisphere). These tropical/extratropical processes have ramped up the relative atmospheric angular momentum (AAM) to the highest values in at least 6 months, at about one standard deviation above the 1968-1997 climatology.
Monitoring of various indicies as well as statistical forecasts suggest this western hemisphere MJO signal will return into the Indian Ocean by late next week. Recent satellite imagery already shows tropical thunderstorm activity increasing across much of Brazil and the Amazon Rainforest, as well as South Africa and even the South Indian Ocean. Thunderstorm clusters are also shifting back westward into the eastern hemiphere from the SPCZ. Past experience would suggest a consolidation of these 2 areas of tropical forcing ~ 60-150E south of the equator late week 2 or week 3. This distribution of enhanced tropical convection would be consistent with La-Nina.
Since this change of tropical forcing would lead to above average easterly flow throughout the tropical and subtropical atmosphere, AAM may decrease to the low values that were observed a few weeks ago. Additionally, the retrogression across the north polar latitudes would also be expected to "hook up" with the tropical forcing, leading to SDM Stage 1 late week 2 or 3.
Most models are already predicting a positive phase of the PNA by later this week through this coming weekend (western North American ridge, eastern trough), with discontinous retrogression during week 2. The latter would result in a western North American trough/southeast USA ridge. Much of the anomalous signal the models are getting is likely coming from the high latitude retrogression, with little predictive input beyond about day 5 from the tropics. I do think the models have the correct general idea, but with little skill in regard to timing and important synoptic details. My preference continues to tilt slightly to the CDC ensemble, especially the week 2 calibrated probabilities. I would have a concern for a strong subtropical jet (STJ) impacting the at least the California west coast by next weekend. Also, the trough may shift back to the west coast, leading to cold/wet events for that region. Whatever the case, blocking across Alaska could set up cross polar flow of true Arctic air from Asia into North America, leading to a cold and wet regime that much of the CONUS has not seen so far this winter (remembering the seasonal cycle as we get closer to spring).
For southwest Kansas, other than the cooling to closer to normal temperatures, still the "same old, same old" dry regime through at least week 1 (~February 13). I have serious doubts of Arctic air making it this far west (not to mention modification due to higher sun angles and lack of snow cover across much of the High Plains). During week 2, we may start to see some changes, especially with better chances of precipitation by next weekend (~18 February). Real Arctic air may make it here (at least shallow) by late week 2 or 3 should there be a situation of a western USA trough and blocking across Alaska. Monitoring is critical, and we need to watch out for "surprises".
Ed Berry
http://www.cdc.noaa.gov/MJO/Forecasts/climate_discussions.html
Slow but important changes are occurring across both the tropics and extratropics. SST anomalies remain below normal across the equatorial central and eastern Pacific, with values at least as cold as -2C and actual SSTs around 24C centered on 145W. Ocean surface temperatures remain slightly above average across the south and west Pacific, with anomalies ~ +.5-1C and SSTs from 29-31C centered near 10-15S/160E. This pattern is reflective of La-Nina.
After 4 months of little MJO variability, during the past couple of weeks or so there has been a coherent but relatively weak signal of the MJO propagating east from just north of Australia to roughly the southern eastern Pacific. One response from this MJO was very intense convection along the South Pacific Convergence Zone (SPCZ) over the warm SSTs this past week. The SPCZ convection added anomalous westerly flow to the tropical and subtropical atmosphere. In addition, feedbacks from the polar latitudes including the wave number 1 retrogressive transient (discussed in previous postings) added anomalous westerly flow to the northern extratropics (with similar behaviors perhaps across the southern hemisphere). These tropical/extratropical processes have ramped up the relative atmospheric angular momentum (AAM) to the highest values in at least 6 months, at about one standard deviation above the 1968-1997 climatology.
Monitoring of various indicies as well as statistical forecasts suggest this western hemisphere MJO signal will return into the Indian Ocean by late next week. Recent satellite imagery already shows tropical thunderstorm activity increasing across much of Brazil and the Amazon Rainforest, as well as South Africa and even the South Indian Ocean. Thunderstorm clusters are also shifting back westward into the eastern hemiphere from the SPCZ. Past experience would suggest a consolidation of these 2 areas of tropical forcing ~ 60-150E south of the equator late week 2 or week 3. This distribution of enhanced tropical convection would be consistent with La-Nina.
Since this change of tropical forcing would lead to above average easterly flow throughout the tropical and subtropical atmosphere, AAM may decrease to the low values that were observed a few weeks ago. Additionally, the retrogression across the north polar latitudes would also be expected to "hook up" with the tropical forcing, leading to SDM Stage 1 late week 2 or 3.
Most models are already predicting a positive phase of the PNA by later this week through this coming weekend (western North American ridge, eastern trough), with discontinous retrogression during week 2. The latter would result in a western North American trough/southeast USA ridge. Much of the anomalous signal the models are getting is likely coming from the high latitude retrogression, with little predictive input beyond about day 5 from the tropics. I do think the models have the correct general idea, but with little skill in regard to timing and important synoptic details. My preference continues to tilt slightly to the CDC ensemble, especially the week 2 calibrated probabilities. I would have a concern for a strong subtropical jet (STJ) impacting the at least the California west coast by next weekend. Also, the trough may shift back to the west coast, leading to cold/wet events for that region. Whatever the case, blocking across Alaska could set up cross polar flow of true Arctic air from Asia into North America, leading to a cold and wet regime that much of the CONUS has not seen so far this winter (remembering the seasonal cycle as we get closer to spring).
For southwest Kansas, other than the cooling to closer to normal temperatures, still the "same old, same old" dry regime through at least week 1 (~February 13). I have serious doubts of Arctic air making it this far west (not to mention modification due to higher sun angles and lack of snow cover across much of the High Plains). During week 2, we may start to see some changes, especially with better chances of precipitation by next weekend (~18 February). Real Arctic air may make it here (at least shallow) by late week 2 or 3 should there be a situation of a western USA trough and blocking across Alaska. Monitoring is critical, and we need to watch out for "surprises".
Ed Berry
Wednesday, February 01, 2006
Regime Transition Madness and our Baby Girl
This posting is to update the current weather-climate situation as discussed during the recent January 25 and 30 postings. The issues written about then are still relevant. Also, please note that data on the CDC web site has not been updated since January 27. The problem is being worked on.
On our January 30 posting concern was expressed about predictability being unusually problematic including the issue of the models prematurely amplifying ridges off the west coast of North America. Two behaviors (discussed below) that we have been monitoring have become robust enough not only to add some credence to a ridge (finally) developing of the west coast, but perhaps signal the initiation of a major regime transition. Most numerical models including their ensembles are coming into better agreement of this evolution as their initial conditions more correctly sample the anomalies contributing to the transition. However, uncertainty of timing and details of this regime change particularly beyond day 3 remains very high.
The first behavior is the high latitude retrogression. During the last few days we have observed the wave number 1 retrogressive transient become more coherent, with the deep low that has been located around Alaska shifting back toward Asia. Feedbacks from this process should allow the EAJ/north Pacific jet to retrace a bit. Thus while the current jetstream remains anomalously strong slamming the Pacific Northwest with several storms, we think that situation may abate starting early next week.
The second observation concerns the behavior of the tropical convection. While stationary forcing remains ~5s/140E, there is a slowly propagating component that has allowed a significant increase of thunderstorm activity to extend east-southeast toward ~ 12s/170W across anomalously warm waters of the tropical south Pacific Ocean. The previous convectively coupled Kelvin wave has lost coherence and decayed. SST anomalies are roughly 1-1.5C above normal from about 10S/160E- 15S/150W with actual SSTs of at least 29C. The tropical convection appears to be located along a gradient of SSTs, and has displaced the SPCZ a bit farther northeast of normal. This SPCZ convection continues to add westerly flow to the subtropical atmosphere of both hemispheres.
Since the propagating convective component has become involved with the southern extratropics, it is difficult to speculate about its future evolution. However, there may be an increase of thunderstorm activity over South America and South Africa, and perhaps the South Indian Ocean, if the signal continues moving east during week 2. This can occur
either through the tropics or midlatitudes via Rossby wave trains and associated jet streak dynamics.
So not only does ridge amplification off the west coast now appear a reasonable scenario by early next week, but there may also be a strong subtropical jet (STJ) undercutting it as well. In fact, should the tropical convective forcing finally evolve into a pattern more typical of La Nina (which continues to strengthen), we may see a "Rex blocking - like" structure of the polar and STJ winds that shifts northwest during weeks 2 and perhaps 3. This would suggest a blocking ridge in the Gulf of Alaska into the Arctic and strong westerly flow at least as far north as California.
The weather impacts would suggest colder and wetter for much of the CONUS particularly week 2 (February 9-15) and perhaps afterwards. In fact, calibrated probabilities from the CDC ensemble are quite supportive of this notion, and can be found at
http://www.cpc.ncep.noaa.gov/products/predictions/short_range/tools/usTlog.CONC11.gif http://www.cpc.ncep.noaa.gov/products/predictions/short_range/tools/usPlog.CONC11.gif
Compared to the predictions above, we would increase pops for above normal precipitation slightly for California and the central/southern Plains. The Pacific Northwest may continue to catch a break. Furthermore, the change toward much colder temperatures would be centered on the north central USA.
Ed Berry and Klaus Weickmann
On our January 30 posting concern was expressed about predictability being unusually problematic including the issue of the models prematurely amplifying ridges off the west coast of North America. Two behaviors (discussed below) that we have been monitoring have become robust enough not only to add some credence to a ridge (finally) developing of the west coast, but perhaps signal the initiation of a major regime transition. Most numerical models including their ensembles are coming into better agreement of this evolution as their initial conditions more correctly sample the anomalies contributing to the transition. However, uncertainty of timing and details of this regime change particularly beyond day 3 remains very high.
The first behavior is the high latitude retrogression. During the last few days we have observed the wave number 1 retrogressive transient become more coherent, with the deep low that has been located around Alaska shifting back toward Asia. Feedbacks from this process should allow the EAJ/north Pacific jet to retrace a bit. Thus while the current jetstream remains anomalously strong slamming the Pacific Northwest with several storms, we think that situation may abate starting early next week.
The second observation concerns the behavior of the tropical convection. While stationary forcing remains ~5s/140E, there is a slowly propagating component that has allowed a significant increase of thunderstorm activity to extend east-southeast toward ~ 12s/170W across anomalously warm waters of the tropical south Pacific Ocean. The previous convectively coupled Kelvin wave has lost coherence and decayed. SST anomalies are roughly 1-1.5C above normal from about 10S/160E- 15S/150W with actual SSTs of at least 29C. The tropical convection appears to be located along a gradient of SSTs, and has displaced the SPCZ a bit farther northeast of normal. This SPCZ convection continues to add westerly flow to the subtropical atmosphere of both hemispheres.
Since the propagating convective component has become involved with the southern extratropics, it is difficult to speculate about its future evolution. However, there may be an increase of thunderstorm activity over South America and South Africa, and perhaps the South Indian Ocean, if the signal continues moving east during week 2. This can occur
either through the tropics or midlatitudes via Rossby wave trains and associated jet streak dynamics.
So not only does ridge amplification off the west coast now appear a reasonable scenario by early next week, but there may also be a strong subtropical jet (STJ) undercutting it as well. In fact, should the tropical convective forcing finally evolve into a pattern more typical of La Nina (which continues to strengthen), we may see a "Rex blocking - like" structure of the polar and STJ winds that shifts northwest during weeks 2 and perhaps 3. This would suggest a blocking ridge in the Gulf of Alaska into the Arctic and strong westerly flow at least as far north as California.
The weather impacts would suggest colder and wetter for much of the CONUS particularly week 2 (February 9-15) and perhaps afterwards. In fact, calibrated probabilities from the CDC ensemble are quite supportive of this notion, and can be found at
http://www.cpc.ncep.noaa.gov/products/predictions/short_range/tools/usTlog.CONC11.gif http://www.cpc.ncep.noaa.gov/products/predictions/short_range/tools/usPlog.CONC11.gif
Compared to the predictions above, we would increase pops for above normal precipitation slightly for California and the central/southern Plains. The Pacific Northwest may continue to catch a break. Furthermore, the change toward much colder temperatures would be centered on the north central USA.
Ed Berry and Klaus Weickmann
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