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.

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