Monday, January 30, 2006

The Baby Girl Needs to Learn

La-Nina continues to strengthen with anomalies of at least -2C and actual SSTs of about 24C, at around 140W. The event is now basin wide with anomalies of -1C and colder covering much of the eastern equatorial Pacific and -4C at ~150m below the surface.

The most significant tropical convective forcing is located near 5S/140E, a bit farther east than typical La Ninas. On roughly January 18, there was a convective flare-up at 0/140E in association with a convectively coupled Kelvin wave moving east at 15-20 m/s. Since then tropical convection has become quite intense across the South Pacific where SSTs are above normal and greater than 29C. Convection is also showing signs of increasing across both northern South America and South Africa. Even though some impacts from the Kelvin wave, when combined with existing SST anomalies, have been "MJO-like", the MJO signal continues weak.

During the past week westerly flow has increased substantially thoughout much of the equatorial and subtropical atmosphere. In fact, relative angular momentum has risen by roughly 2 standard deviations with respect to the 1979-1998 climatology. Much of this increase, the largest in about 6 months, has come simultaneously from several mountain barriers across the globe. In the posting I did January 25, there was discussion of retrogression across the north polar latitudes, and an ongoing sudden stratospheric warming (SSW). Feedbacks from the latter may also be a factor in explaining the recent changes in the high latitude zonal mean flow.

So, my thoughts are that the circulation is currently transitioning to SDM Stage 3, even though we have La Nina. That includes the continuation of a strong extended EAJ aimed at the west coast of the USA. There is a possibility the storm track may shift south by next week (timing is very uncertain), even though the greatest impacts are currently across the Pacific Northwest.

As has been the case for at least the past couple of weeks, many models have wanted to build a ridge off the North American west coast after about forecast day 5 (starting this upcoming weekend in today's case). I have wanted to believe some of those solutions, which would be suggestive of colder temperatures for much of the country for week 2, and a cessation of the frequent storms hitting the Pacific Northwest. Well, that has not happened. Furthermore, research suggests there may be lower predictability in La-Nina regimes as complicated as this one. Varying model solutions from day to day demonstrate that. Thus I would be cautious of model solutions that build ridges off the west coast after day 5. Instead, I expect a continuation of progressive synoptic systems to be more probable.

If there are to be adjustments to the circulation across the Asia-North American sector more consistent to La-Nina (SDM Stages 1 and 2), one behavior I would want to see is a rapid intensification of tropical convection across the Indian Ocean. I would also like to see an overall westward shift from it's current location to perhaps 100-120E. The above discussed Kelvin wave remains coherent and is approaching the Indian Ocean.

For southwest Kansas, other than progressive Pacific storm systems producing light precipitation from time to time, I see nothing substantial for at least the next 2 weeks. Given the seasonal cycle, temperatures may return to near normal during week 2.

Ed Berry and Klaus Weickmann

Wednesday, January 25, 2006

The Little Girl is Growing

The current circulation state continues to be a most trying time for me, both as scientist wanting to understand it and trying to make week 1-2 predictions. Recent events include a continued cooling of central and eastern Pacific SSTs, with anomalies lower than -1.0C extending from just west of the date line to 120W, with lower than -1.5C covering a good portion of that area. Anomalies as low as -5.0C extend to depths of roughly 150m at 140W per latest data from the TAO buoy array. The atmospheric response continues to become more impressive. Assisted by a recent tropical convective flare-up near 0/140E (linked to a convectively coupled Kelvin wave) discussed in previous postings, robust twin subtropical cyclones are present just east of the date line, while anticyclones remain stationary near 120-140E. Finally, measures such as atmospheric angular momentum (AAM) remain very low, at least 1.5-2 standard deviations below the 1968-1997 climatology. This low AAM is the result of deep zonal mean easterly flow covering much of the subtropics as well as the Arctic. What all this tells me is that our cold event (La Nina) is getting stronger, and, among other things, the Walker circulation may be becoming enhanced (part of coupling between the atmosphere, SSTs and tropical convection).

Meanwhile, the extratropics continue their ritual of making life tough for meteorologists. The much talked about SSW (which is still going on) has propagated into the troposphere, and, instead of creating a wave zero distribution in terms of an anticyclonic wind anomaly north of 60 deg, a wave number 0/1 has developed. While a lobe of the polar vortex covers Alaska, a large anticyclone (with height anomalies in excess of 35dm) covers most of northern Asia and Scandinavia. The interactions of our La Nina base state (with the tropical convection centered around 10S,130E), on-going fast wave energy dispersions throughout the midlatitudes and the wave 0/1 pattern at high latitudes has not only allowed for more cold air to surge into the South China Sea, but also across the east Pacific Ocean. Additionally, the EAJ is extending across the Pacific once again, but farther north than we saw in December and earlier this month. There also continues to be this little understood mechanism of feedbacks which include the persisting of old anomalies from December.

So, what happens next? Will some of the bitterly Arctic air from Alaska and the northwest territories of Canada come into the CONUS during week 2 (roughly first week in February)? I can tell you (once again) that uncertainty at least for making predictions for the Pacific-North American sector beyond about day 3 is as high as it gets, and that the numerical models do not appear to be representing the impacts onto the circulation from the tropical convective forcing (including La Nina) very well after about day 5. My thought is that, and most models do show this, the wave 0/1 component at the high latitudes will move west (as it should per Rossby wave dynamics). Thus at least that "part of the atmosphere" may have some numerical predictability. If that is the case, more cold air is going to continue to be transported into the north Pacific from both east Asia (lots of cold air over there) and Alaska.

Well, here we go again, only this time in the presence of a more mature La Nina response. We think the north Pacific jet may once again become anomalously strong by week 2, but perhaps not quite to the extent we saw in December. Many of the models are also suggesting this, which we should respect since we got burned by this back around early-mid December. What happens over North America, you tell me. Given that the twin subtropical cyclones mentioned above would be expected to also move west, and the ridge component of the high latitude retrogressive transient may be across the Pacific, a full-latitude ridge may amplify just off the North American west coast starting roughly next weekend. That would favor that transport of cold air into the CONUS that I have been discussing for the past 2 weeks which has yet to happen (if ever).

For southwest Kansas, still the "same old-same old" for at least the next 10 days; dry and warm. There may be a couple of episodes of very light precipitation, but nothing significant. During the 10-14 day period (February 4-8), perhaps a return to more seasonal temperatures, but with not much hope for decent precipitation.

Ed Berry

Sunday, January 22, 2006

Current Atmospheric Circulation: Rogue or Linear?

The matters that I discussed on the January 18th posting are still extremely relevant. We are simply at the point where all that can be done is monitor, particularly if and when a sudden amplification of the westerlies across the Asia-PNA sector occur. The details of what the outcome of such kind of event are unclear. However, the most probable solution would be a western Pacific trough, central-east Pacific ridge with a downstream trough across western North America by roughly 7-14 days from now (30 January - 6 February). Brief justification for this possibility is given below.

During the past week the tropical convective forcing became concentrated and very intense centered roughly on the equator/140E (north of Australia). Anomalies less than -90 w/m**2 were observed, and may have been the result of a convectively coupled Kelvin wave merging with convection moving northwest from the south Pacific. This flare-up has already impacted the circulation, initiating, for example, a Rossby wave energy dipersion linked to a couple of recent storm systems across the USA. The stationary tropical forcing has increased in areal coverage the last couple of days, extending from the eastern Indian Ocean to just northeast of New Zealand. MJO activity is nil to very weak (indicies such as the Wheeler phase space plot are not representative), and the atmosphere continues to respond to at least weak La-Nina conditions (equatorial SST anomalies have cooled to less than -1.5C around 140W January 21).

At this time a very fast synoptic wave train moving though the subtropics of the eastern hemisphere is interacting with the tropical convective forcing. Upper tropospheric divergent outflow from this thunderstorm activity is quite impressive, and will pose a difficult predictability problem for all the operational numerical global models. Today and for the past several days all model forecasts have been quite varied, generally suggesting a low amplitude flow with progressive synoptic systems. The CDC ensemble from 0000 UTC 22 January 2006 initial conditions does suggest a large amplitude version of the scenario given in the first paragraph. If the atmosphere responds as "linear thinking" would suggest, the CDC ensemble solution would be reasonable. The latter is given by SDM Stage 1, and, in this case, would project onto negative phases of the PNA, AO and NAO (polar latitude Stratospheric easterlies have already propagated into the Troposphere due to the recent SSW). A transition to SDM Stage 2 would then be expected (ridge closer to west coast of USA going into week 3).

As we all observed during the last 2-3 weeks of December continuing into this month, the atmosphere went "rogue", and the jet expanded all the way from north of India to the west coast of the USA (anomalies in excess of 40 m/s, at times). This event was about as extreme (nonlinear) as anything can get, and it would be interesting to attempt to reproduce this jet in a general circulation model (GCM). As a note, utilized along with our SDM, it would also be nice to run climate models in near real-time. In any event, in regard to making a prediction for days 3-20, I have to go with what linear meteorological thinking tells me. That would be at least a low amplitude version of the circulation predicted by the CDC ensemble. Future model runs must also be carefully monitored.

All of the above suggests a possibility of a sharp weather change for much of the lower 48 states during week 2 (starting next weekend). The western half-two thirds of the country may cool to below normal temperatures due to Arctic air, while the southeast stays warm. Synoptic systems may stay progressive, with perhaps an active storm track with high impact weather from the Pacific Northwest into the Rockies, then northeastward across the Plains. Given tremendous uncertainty, I do not want to give any more details.

For southwest Kansas, given our location, there is not much I offer in regard to real hope for much needed significant precipitation. This upcoming week looks "same old-same old"; above normal temperatures and basically dry. The notion of another weak storm with light precipitation for roughly Thursday appears reasonable. For the period of next weekend through February 6th, temperatures may lower to at least normal, with perhaps an episode or 2 of well below normal temperatures. However, I am still concerned about storm systems being too progressive to give us much precipitation. For locations to our east and north, such as eastern Kansas into Iowa, lots of snow may occur.

Ed Berry

Wednesday, January 18, 2006

Resurrection of Winter (for the USA)?

The emerging La-Nina (with SST anomalies -1.0C and lower along the equator from 170W to near South America) has already impacted the circulation state of the atmosphere. This includes persistent tropical convective forcing centered just northwest of Australia, relative AAM about 2 standard deviations below the 1968-1997 climatology, and zonal mean westerly flow shifted poleward of normal. Additionally, bitterly cold Arctic air has been expanding not only across much of Asia, but also Alaska and northwest Canada. This base state circulation is represented by SDM Stage 1 (see previous posts for link), and these initial conditions are relevant for any upcoming predictions through at least week 2 (February 1).

In addition to other forcing-response processes discussed in previous writings, the recent Sudden Stratospheric Warming (SSW) 0f at least 30 deg C must also be given consideration. In summary, SSWs disrupt the circulation of the winter Stratospheric polar vortex by producing easterly wind anomalies. These easterly anomalies can and do propagate into the Arctic troposphere, and contribute to rising heights/pressures. The latter can lead to a projection onto the negative phase of the Arctic Oscillation (AO). The recent USA Hazards Assessment issued by CPC also discusses this concern, and additional information on the AO can be found at

With the EA jet having retracted, our thought is the north Pacific storm track will be directed to the west of the Aleutians, allowing for a ridge to amplify initially across the central and east Pacific by early-middle of next week. Storms would continue to impact the Pacific Northwest. Considering the current location of the tropical convection (centered ~10S/135E), there is concern the atmosphere may transition into SDM Stage 2 by roughly next weekend. That suggests a possibility of an east Pacific ridge to link up with positive height anomalies all across the Arctic (which would extend into the North Atlantic; i.e., negative phase of the NAO), and allow for the delivery of Arctic air particularly into the central USA (centered on the northern Rockies and Plains). While the west coast would become dry, the weather may be quite active across at least the eastern two-thirds of the country. Uncertainty remains very high with this scenario. However, many models are starting to pick up on this notion, particularly the GFS ensemble and ECMWF deterministic run (1200 UTC 18 January initial conditions).

For southwest Kansas, if winter (at least in terms of well below normal temperatures) is to return, that may not occur until later next week. In the meantime, after one weak storm goes by this Friday, another rain/snow event is possible on about Sunday-Monday. Perhaps a decent precipitation situation (still low optimism) may be possible around Wednesday-Thursday of next week (25-26 January). It may be after this storm that the circulation transitions to SDM Stage 2, meaning the possibility of Arctic air spreading across the Plains.

Ed Berry

Sunday, January 15, 2006

The Atmosphere has hit the Brakes

With respect to 1968-1997 climatology, the current global tropospheric relative atmospheric angular momentum (AAM) is about negative 2 standard deviations, perhaps the lowest we have seen for at least a year. This means that the global circulation is dominated by deep anomalous zonal mean easterly flow, much which is coming from the subtropics. Any above average westerly flow can only be found in latitude bands around 45N and 50S. Much of this low AAM has been forced by the tropical convection, with the primary region having shifted westward from roughly 130E to 80E over about the past 4 weeks. Currently the convection extends in about a 20 degree wide band from the central Indian Ocean to the south Pacific, centered just north of Australia.

One response has been a significant retraction and weakening of the east Asian/north Pacific polar jet stream since about January 4th, 2006. As discussed in previous postings, the jet was extended from north of India to the west coast of the USA, with wind speed anomalies in excess of 70 knots, at times. Currently the strongest winds are generally present from north Africa to east Asia, with much weaker anomalies. A time-longitude section (Hovmoller diagram) of 250mb wind speed anomalies between 25-40N demonstrates this point.

With the polar vortex becoming displaced toward Asia, a general east Asian trough, central/east Pacific ridge and western USA trough pattern, with embedded progressive synoptic systems, has evolved within the above discussed basic state. This is typical of a La-Nina situation, and is represented by SDM Stage 1 (see correct link below).

An important question to ask is if there will be any synoptic amplication? Monitoring tools would suggest roughly in about 10 days, meaning next weekend into week 2 (~January 22-29). The details of this amplification are unclear. Given the current location of the tropical convection, the possibility of a transition into SDM Stage 2 also needs be considered. Stated with very low confidence, after a Rockies and Plains storm event by about next weekend and maybe again week 2, a large amplitude ridge may develop just off the west coast of North America extending into Alaska by late week 2. This would favor transports of Arctic air particularly into the middle of the country by then. Some ensemble members of the models may be capturing this scenario (ex., GFS and Canadian).

For southwest Kansas, a record warm January is in progress, and I still cannot be optimistic about widespread significant precipitation given the progressive nature of synoptic features. However, temperatures should trend down this upcoming week, and the storm for about this Friday may slow down enough for measureable snowfall. We may see 1-2 other opportunities week 2. It must be remembered this time of year is typically dry for this part of the world. In fact, I can easily argue we are seeing enhanced climatology with the zonal mean westerly flow now shifting poleward of normal.

Ed Berry

Wednesday, January 11, 2006

Changes are for REAL

In my January 7 posting, I discussed recent behaviors (please review, if needed) that could lead to circulation change, to that as depicted by Stage 1 of our Synoptic-Dynamic Model of subseasonal variability (SDM). This stage favors troughs coming into western North America. Indeed, that circulation change is occurring, only to mature during the next couple of weeks. As a quick review, factors leading to this change include robust tropical convection across the Indian Ocean (not a MJO), and lowering pressures/heights across the polar latitudes. The impacts from Stratospheric-Tropospheric interactions over the Arctic in regard to making any week 1-2 predictions are definitely unclear for our current situation. Intense tropical thunderstorm activity across the south Pacific is contributing to STJ activity across the east Pacific, which may also be important for future western USA troughs/storms.

I continue to like the general scenario given by the CDC and NCEP ensembles (other models are getting on the same general path). One storm looks likely across the Rockies and Plains during about the Sunday-Wednesday period (January 15-18). This system looks to bring heavy precipitation first across much of the west coast, heavy snow across the Rockies, and perhaps intense thunderstorms over the south central and southeast states.

Based on monitoring, I think there may be a more significant trough along the west coast during much of week 2 (January 18-25). That latter would be part of a trough-ridge-trough pattern across the PNA sector. Beyond stating the above, details are unclear. Probilistically, perhaps 2-3 synoptic systems would first impact particularly California, and then move through the Rockies and subsequently turn northeast through the central part of the country. High impact weather concerns from this option include heavy cold sector snowfall and severe thunderstorms in the warm air. While some Arctic air would likely bleed southward into the northern Rockies along with colder than normal temperatures across much of the west, the eastern states should experience above average temperatures. Whatever the case, we need to monitor!!!

For southwest Kansas, I continue to express the concerns about systems being too progressive, etc., as I did on January 7. HOWEVER, I am definitely encouraged about opportunities for precipitation starting with the Monday storm. Even though the most significant precipitation will likely be off to the east and north, a period of some measurable snowfall with lots of wind needs to be a concern. Temperatures should then warm rapidly to above normal levels (along with dry) by the middle to late part of next week. By next weekend (January 21-22), that trend may change tremendously. PROBABILISTICALLY, our circulation state may allow for closed/slow moving lows to develop across the southwest states by that time. That would allow for more time to get moisture transport from both the Gulf of Mexico and eastern Pacific STJs, with subsequent increased precipitation chances.

Ed Berry

Saturday, January 07, 2006

Finally Some Hope

For the last several days I have been monitoring several slow evolutions concerning features such as the tropical convective forcing, the accumulation of cold Arctic air across central Asia, atmospheric angular momentum, and the strength of the east Asian/north Pacific jet. The primary region (other secondary regions understood) of tropical convective forcing has been spreading westward across the Indian Ocean, and recent satellite imagery has it centered at roughly 5S/110E. However, for the first time since late November 2005, there is respectable thunderstorm activity across the western Indian Ocean. The latter may be linked to both forcing from the extratropics and seasonal cycle. Impacts from this slowly changing distribution of tropical heating have seemingly allowed the east Asian jet to both weaken and retract, as well as persist cold air across much of northern and central Asia. Hence I think, both in terms of the circulation and all measures of dynamic forcing, still stated with low confidence, SDM Stage 1 is most probable to develop week 2 (~15-21 January). Please see for details on the SDM.

For the Pacific/North American sector, I think we will see a slow retrogressive pattern of the current western USA ridge/eastern trough (with amplitude variations). This is likely to involve at least 2-3 synoptic events, and I like the scenario depicted by the CDC ensemble. In general, the changing initial conditions due to the above mentioned responses may already be getting sampled by most numerical ensemble prediction systems, and agreement of a transition to SDM Stage 1 during week 2 is improving. My experience with timing of these kinds of behaviors would suggest a decent western USA trough by days 10-14 (period of January 17-21, and into week 3???)

HOWEVER, since models will not predict tropical convection and circulation responses very well after about forecast day 5, monitoring is critical. An astute forecaster will watch for sudden flare-ups of thunderstorm activity across the south Indian Ocean, and possible subsequent amplification of wave trains moving rapidly eastward through southern Asia, linked to twin subtropical anticyclones centered ~90-120E. A concern from a situation such as this would be for a deeper than predicted western USA trough in ~5-7 days afterwards.

For southwest Kansas, I would still predict above normal temperatures with little precipitation through at least the end of next week (sprinkles, etc., understood). For week 2 (January 15-21), while I would be favorable for above normal precipitation for states east and north of here, there is a concern that individual synoptic systems are still going to be too progressive for this part of the country. I would be worried about dry intrusions and tropical moisture transports being shunted to our east, for example. Ideally, we need to have "closed lows" remain stationary (before coming out) over the so-called desert southwest (roughly AZ) for a few days, allowing moisture transport from both the east Pacific and Gulf of Mexico. In any case, we may get into a situation of some Arctic air bleeding east of the Rockies with southwest flow "aloft", perhaps meaning some light precipitation and a change toward colder temperatures. We will see what happens.

Note, since I will be on travel next week, I may not be able to do another posting on this Blog until the week of 16-20 January. Also, for the record, the posting, "Throw the RED Flag", was on January 4th, 2006, not December 31st, 2005. Hopefully this writing will have the correct date and time posting.