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

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