This weekend temperatures are expected to drop dramatically as a Pacific storm system and it's unseasonably strong 165+ kt jet affect the west coast this Friday into Saturday. If this morning's 12z GFS verifies, as much as 3-4 inches of precipitation could occur in the mountains of Northern California, Oregon and Washington. At high elevation some of this precip could be in the form of snow.
The front associated with the trough is currently forecast to hold together south of Pt. Conception and could produce some showers in the Los Angeles area on Saturday, particularly in the mountains. A BUFKIT analysis of 12z GFS data generates about 0.3 inch of rain at Van Nuys, but given the time of year, and the ample time remaining between now and Saturday, we'll have to see!
Ed Berry first mentioned the possibility of an "anomalous extended North Pacific Ocean jet collapsing into a western USA trough" in a September 6, 2008 post on Atmospheric Insights, and refined the projection, including a timeframe, in subsequent posts.
Update 10/06/08. Saturday's trough and front behaved about as expected with scattered light rainfall around the area. Precipitation amounts generally ranged from a trace or less to about 0.1 inch or so in some foothill and mountain locations.
Update 10/03/08. Focus of the incoming storm system continues to be Northern California and the Pacific Northwest. A BUFKIT analysis of 12z NAM data shows the expected north to south gradient in projected precipitation. About 0.5 inch is projected at Monterey, 0.2 inch at San Luis Obisbo, 0.1 inch at Santa Barbara, and 0.06 inch at Van Nuys. The 09z SREF Ensembles suggest a high probability, low precipitation event in the Los Angeles area with about a 90% probability of more than 0.01 inch of rain, but less than a 10% probability of more than 0.1 inch. We'll see!
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