Wednesday, March 15, 2006

Short Update

Please refer to previous postings for links. Due to travel, I may not be able to write another discussion until at least a week from now (March 22), and this posting will be relatively brief.

The MJO signal is still very weak. Since my March 11 posting, tied to persistent tropical convective forcing centered on Indonesia (~0/120-140E) zonal mean anomalous easterly flow has increased throughout the tropical and subtropical atmospheres, particularly south of the equator with anomalies of ~minus 10 m/s. For the northern hemisphere (NH) zonal mean anomalous westerly flow has actually shifted south to ~30-40N with easterlies across the polar latitudes. The latter is linked to yet another anticyclonic gyre predicted by the models to retrograde from Scandanavia into Canada and Alaska during the next 2 weeks (which is reasonable). Combined with below normal sea-level pressures across major NH north-south mountain ranges (particularly east Asia), these behaviors created a large negative tendency of global relative atmospheric AAM on about March 10. Currently the global relative AAM is at least 3 standard deviations below the 1979-1998 climatology, the lowest in 2 months. A baroclinic wave packet tied to the negative AAM tendency is currently approaching the USA west coast, and will lead to closed low development across the southwestern states by this upcoming weekend.

During the last 3-5 days tropical convection has rapidly intensified across the anomalously warm waters of the equatorial IO. My thought is this region of convection may move east only to persist the Indonesian convection. The characteristics of the current circulation and tropical forcing suggest SDM Stage 4 is most representative of the weather-climate situation. SDM Stage 1 would be most probable during the next 1-2 weeks. As stated before, we are in a situation of both stationary boundary forcing and circulation response with embedded synoptic variability, taking into consideration the seasonal transition into boreal spring.

As shown by most models, the high latitude retrogression will set up a split flow pattern across the lower 48 states, leading to an anomalous ridge across central Canada and a developing storm across the southwest USA by this weekend. After some "shifting around", my thought is during week 2 the situation of strong and anomalously cold troughs hitting the west coast of North America leading to baroclinic storm development on the USA Plains will return. This all means a continuation of an active weather pattern for much of the country, suggestive of more severe storms and heavy rainfall from the southern Plains into the Ohio Valley, cold and wet for much of the west, winter precipitation and thunderstorms from the northern Plains into the Great Lakes, etc.

Southwest Kansas has some hope for precipitation this weekend, particularly Sunday into Monday. How much will depend on the track of the above discussed southwestern closed low. I am worried that as we go into week 2 (and 3) there may be 1 or 2 situations similar to what was observed on Sunday, March 11 (strong southwest (high) wind and blowing dust). It is probable most of the precipitation will again be to our east and north. However, lets see if the "seasonal cycle can help start to slow down" the recently observed fast movements of the synoptic lows from the Rockies into the Plains. After colder than normal temperatures for week 1, above normal readings are probable for week 2.

Ed Berry

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