Friday, January 05, 2007

Update on our ENSO/MJO and Then Some Atmosphere

Because of my preparations to spend the first of 2 months at ESRL/PSD in support of the HMT project, I am unable to do a complete posting today. However, my discussion and predictive thoughts from last week (12/29/06) look very much on track. The tropical convection across the Eastern Hemisphere centered ~0/130E is becoming less coherent spatially. A convectively coupled Kelvin wave is leading to a flare-up over the warm SSTs near the date line and there is some evidence that the MJO component may be stalling ~140E. The trade wind surge east of this forcing has led to some cooling of the SSTs and I think our warm ENSO has peaked (which is consistent with seasonal cycle considerations). I have a thought going into weeks 2-3 there may be tropical convection “all over the place” with one region from the South Pacific-eastern Indonesia while South Africa-Indian Ocean and northern South America become active (along with the SACZ).

The East Asian cold air surge directly linked to the tropical forcing is occurring as I type. This will lead to the reverse PNA pattern by the end of next week (through downstream propagation of baroclinic wave energy and excitations of Rossby waves) with then a slight eastward shift by the end of week 2 (GSDM Stages 1-2). Most models show this. There are a few solutions that suggest this regime to breakdown quickly during week 2 (ex., the Canadian), and I think that is unlikely. Blocking structures across the north polar latitudes are a real possibility as these evolutions occur. In fact, as we go into weeks 3-4, I have a thought that as our combined extended anomalous jet becomes established across the North Pacific ~35N, there will be “undercutting” of blocking across Alaska. Given the multiple regions of tropical convective forcing which may be present by that time, my own thoughts would be for a GSDM Stage 3-4 like response, in many ways similar to December 2006 (which led to the intense closed lows across Desert Southwest).

In terms of the weather, a cold (with Arctic air) and stormy regime for much of the western and central USA looks very probable by week 2 (southwest flow storm track on the Plains) possibly lasting into week 3. The west coast should be generally dry (weak systems understood) while the Deep South remains warm. After week 2 (after ~ January 19th) intense fairly low latitude westerly flow may slam into the California coast leading to high-impact precipitation events there. Much of the rest of the USA should have moderating temperatures (there may still be an Arctic cold air source) while locations from the central/southern Rockies into the Mississippi and Ohio Valleys remain active.

Of course, who really knows what the exact timing will be and let’s just see what happens. I will try to start my more frequent/short postings ~Monday-Tuesday of next week.

Ed Berry

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