In the past week the weather models have been all over the map -- and sometimes off of it -- trying to come up with a forecast for this week and the Thanksgiving holidays. Now that a potent looking upper level low system is bearing down on the Southland, the 18z NAM and 18z GFS both agree we are going to get drenched.

The Hydrometeorological Prediction Center (HPC) is projecting from one to two inches of rain over a large area of Southern California. BUFKIT analysis of 18z data for Van Nuys generates rainfall totals of in excess of 2 inches for the storm. Depending on the strength of the southerly inflow, rainfall totals could be higher on south facing foothill and mountain slopes.

Radar is already showing some echoes aloft, and some showers could occur overnight and into tomorrow. Rain is expected to begin in earnest during the day tomorrow, perhaps as late as tomorrow afternoon or evening, and taper off late Wednesday night into Thursday morning.

NOAA has just released their 2008-2009 Winter Outlook. The precipitation outlook for December through February indicates an equal chance of below normal, near normal, or above normal precipitation for California. The IRI Multi Model Seasonal Forecast for Dec-Jan-Feb indicates below average precipitation is slightly more likely in southern third of California.

Update 11/25/08. BUFKIT analysis of 12z NAM and GFS data for Van Nuys isn't quite as wet as yesterday's 18z run. Over the next 36 hours, the 12z GFS generates about 0.8 inch, and the 12z NAM about 1.7 inch of rain, with maximum rain rates of about 0.4 inch/hour. Rain is expected to move into the Los Angeles area later this afternoon or evening.

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