Saturday, December 31, 2005

Changes: Real or (my) Imagination?

The beat goes on today with our extended north Pacific Ocean polar jet stream and split flow/ridge conditions across the Rockies and Plains. While the west coast has received plentiful precipitation for at least the past week, wild fires have raged across the southern Plains. Will this situation persist?

Well, we have been stating (like an "old broken record") the extended Pacific basin EAJ is not consistent with where the tropical convective forcing has been (centered ~10S/120E), at least in a composite sense. However, careful monitoring suggests that various feedbacks have resulted in a "MJO-like" convective signal across the western hemisphere (WH). At the time of this posting the signal was at about 10S/60W and propagating east at around 10 m/s (~ 8 deg long/day). If this feature propagates coherently, it would reach the Indian Ocean in about 2 weeks. Thus there appears to be a "MJO-like" behavior superimposed upon our stationary eastern hemisphere (EH) tropical convective forcing. At least 2 objective tools verify this notion.

A convective signal coming back into the EH along with the on-going slow weakening of other various nonlinear physical feedback mechanisms suggests our Pacific jet should contract during the next couple of weeks. The atmospheric interactions which could allow this scenario to occur are already present, and various models have started to capture them in their initial conditions. The CDC ensemble has taken the lead, while other prediction systems such as the NCEP GFS and Canadian ensembles, and the ECMWF single run are trending (does not mean this is right).

The gist is I like the notion of ridge amplification along 120W by the middle of next week, with the possibility of discontinuous retrogression of the ridge position into the eastern Pacific after day 10. However, I have been suggesting this evolution (ridge back into east Pacific) for "one reason or another" for roughly 2 weeks, and what has occurred instead is the EAJ slamming into the west coast with storm after storm (the atmosphere is a great teacher). So, let us continue to monitor, and watch for behaviors such as more tropical convection developing across the south Indian Ocean (~60E) and merging with the persistent area farther east (~120E), the polar vortex becoming displaced toward central Asia (~90-120E) instead of the date line, and consistency with various model runs suggesting a ridge retrogression to ~140-150W.

For southwest Kansas, other than temperatures cooling toward climatology by the end of next week, no big changes. In fact, temperatures appear likely to warm again to above normal levels by next weekend into the following week. Little, if any, precipitation is in sight through at least on the order of January 10, 2006 not only for southwest Kansas, but for much of the central and southern Plains. (BIG) Maybe (with lots of uncertainty) some hopeful changes for precipitation will be seen in about 2 weeks. It will take a lot to impress me.

Ed Berry

No comments: