2007-01-29 Wx Forecast and Discussion
Current conditions
The southwesterly flow of 500 mb cut-off low remains far south of the ARB. It is, however, moist enough to produce 0.5" rainfall amounts near Oxnard and southward.
Surface conditions are pretty much unchanged in the ARB. Fog is reported in the Valley with temperatures in the low 30s at 12 UTC. Temperature at Blue Canyon and Forrest Hill is in the mid to upper 30s. At higher elevation, where there is snowpack, the temperature is well below freezing.
00-72 Hour forecast
The chances of precipitation in the ARB remain slim over the next 72 hours. It is possible that some cloudiness and light precipitation could occur in spurts as short waves and cloud packets revolve around the cut-off low. Precipitation amounts would be at most a few tenths of an inch, but the more likely scenario is that a few high clouds will move over the ARB without producing precipitation.
3-10 days
Tropical moisture is making its way across the Pacific, within the 20N to 30N latitude band. The GFS ensemble continues to point at Feb 4 as the earliest day of potential interest, looking more like a cold event than an atmospheric river. A pool of IPW > 35mm air develops west of California about Feb 3, so that one can't rule out the possibility a small whirl could break from the larger trough and tap into that moisture pool to form a sort of mini-atmospheric river (call it an atmospheric creek? or tributary?). The more interesting period looks to be Feb 6th and beyond.
Quite a bit of discussion concerning the forecast beyond 10 days during the HMT coordination call. Ed and Klaus provided plots in another blog entry that suggested a wave train that extends across the Indian Ocean into the western Pacific may continue to connect itself with the subtropical and extratropical jet stream, causing the west coast ridge to retrograde. They believe the GFS solution probably will not be able to simulate this connection correctly, but that other ensembles, particularly those generated at PSD, have solutions consistent with the scenario of a retrograding ridge. Beyond day 10, another MJO may form as a wave packet moves off the African coast into the Indian Ocean.
Chris Anderson GSD/FAB