2007-01-25 Wx Discussion and Forecast
2007-01-25 HMT Wx Forecast and Discussion
New forecaster today. No more bad dreams.
At 12 UTC, a 500 mb trough is positioned just off the N CA coast. Despite this normally favorable condition, the 700 mb and surface flow remains very slow and without a significant upslope component. Furthermore, IPW at Bodega Bay is between 0.3 and 0.4 inches.
Beneath the stagnant flow, fog is evident in the Valley where temperatures are in the mid 30s. Temperature at Blue Canyon and Forrest Hill are 48 and 43, respectively, where the snow pack is zero. At higher elevation, where there is snowpack, the temperature is just below freezing.
00-72 Hour forecast
There is no chance of precipitation exceeding a few tenths in this time period. The main weather feature is the low positioned offshore near N CA. This feature is forecast to wobble, but without ingesting any Tropical moisture.
The GFS ensemble contains some precipitation in the ARB area in days 3-5. It is entirely tied to this wobbling low. The ensemble brings IPW values between 0.5 and 0.7" inland as the low wobbles onshore. Three-hour precipitation amounts do not exceed a few hundreths of an inch, however.
Things get interesting beyond 5 days. There is a shift in the Polar jet stream that is reminiscent of a shift that occurred in early December that lead to a couple of IOPs. The long range GFS shows a shift in the location of polar air beginning Jan 29-30, such that cold air and very strong upper-level vortices are expected to move across the Siberian plains and northern China. The result is a succesion of powerful waves moving across the Pacific Jan 31 through the end of the forecast guidance on Feb 8. There are two differences between this pattern shift and the one that occurred in early December. First, the Tropical convection is kicking in gear near 120E and providing a stream of moisture into the Westhern Subtropical Pacific. Second, the pattern established across the Pacific is less zonal but consisting of more prominent storms than in early December. This leads me to think that the chances of a "big one" are improving. It seems plausible that a stream of Tropical moisture could be carried eastward with one of these large amplitude storms.
The timing of the first storm of interest appears to be Feb 2 or 3.