2006 -01-07 WX Discussion and Forecast
The ridge over western US is rapidly collapsing with heights increasing across the mid-Pacific. This is speeding up the steering flow and decreasing the amplitude of waves in the Pacific. As a consequence the NW US is being hammered by a series of minor amplitude fast moving waves that will impact the coastal areas from Washington to northern California. These systems will flirt with the ARB, brushing by to the north. The short wave that moved through today will be followed by one this evening (8/03GMT). This longwave readjustment is playing havoc with the model’s handling of systems, so there is less consensus today than yesterday.
The wave we expected for Wednesday (11 Jan) from yesterday’s GFS is forecast to come in as two separate minor short waves that will drive an IPW plume toward the coast, arriving early Tuesday (10/09GMT) and another minor trough (imbedded in larger scale warm advection) and moist surge for Thursday (12/06GMT). Most of the dynamic forcing goes north of the ARB with orographic lift on the Coast range of northern CA and Oregon. Only minor precipitation amounts are predicted by the GFS for the ARB. This solution favors what the ECMWF was saying yesterday: weak system Wednesday, strong system Saturday. I was unable to look at the ECMWF for today. All the models (GFS, UKMET, NOGAPS and CMC) vary the timing on these minor waves, but all agree that the “big” event we were expecting for Wednesday probably won’t pan out. The IPW plume lingers off the coast from Wednesday to Saturday, with occasional surges into the San Joachin Valley, so RHs will remain elevated in the ARB area. The problem is no dynamic or orgraphic lift.
The event for next Saturday-Sunday(14 Jan ) is still present in some of the models although there are some differences in timing, and intensity. A majority of the GFS ensembles still support a major trough on the coast in that period. However, a few support a closed-off low and blocking pattern. If the model majority wins out, there may be a period of warm advection with an associated IPW plume late on Friday (13 Jan).
John McGinley