Wednesday, December 14, 2005

Ridge Busters on the Way???

I do think our large-scale baroclinic development event across the Pacific is going through its life-cycle, leading to the current amplification of the ridge off the North American west coast. A portion of the tropical convection has moved eastward to ~10N/160E, perhaps as a response. There is also a flare-up of thunderstorm activity around 10S/160W along the South Pacific Convergence Zone (SPCZ) due to the warm SSTs. However, the core remains centered along the equator and about 110E per satellite imagery.

Nearly all models currently suggest the north Pacific jet to outrun the convection, and impact at least the northwest USA and BC by about the middle of next week. I do think that notion is reasonable. If we do get a nice linear response to the tropical forcing, this jet should then move southward, and bring troughs into the western states by mid-late week 2 (24-28 December; go into SDM Stage 1). However, there is a tendency (seasonal cycle considerations) for these extended north Pacific jet structures to persist during winter. In fact, the single deterministic run of the ECMWF based on 1200 UTC 14 December initial conditions valid 24 December (240hrs) does show SDM Stage 3. The lobe of the polar vortex is predicted to be displaced toward the date line with split flow across North America and central Asia (and strong westerlies across the Atlantic).

If the ECMWF prediction of the circulation should verify and then persist, what gives? Again, this would not be in concert with the tropics and an overall global atmospheric circulation currently characterized by anomalously low relative atmospheric angular momentum (AAM). That is, below average westerly flow. We just need to closely monitor everything daily.

Folks is southwest Kansas can expect this upcoming weekend to colder than normal with light precipitation. By the mid to late part of next week and probably through Christmas weekend, above average temperatures with little, if any precipitation, appears most probable at this time.

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