# Friday, March 18, 2011
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HPC 3-Day Precipitation Forecast
For the Period Ending 11:00 a.m. Monday, March 21

Along with January and February, March is one of the big three precipitation months in Southern California in which the average rainfall for Downtown Los Angeles exceeds 3.0 inches. In January we were about 2.5 inches below normal rainfall, and in February about 0.4 inch below normal. So far this March, we're nearly two inches below normal for the month. If it were not for an unusually wet December in which Los Angeles recorded 8.32 inches above normal rainfall, we'd be looking at 50% water year right now instead of over 100%.

If today's 12z NAM and GFS forecasts verify, we could make up that March deficit, and push our water year total up to nearly 120%! According to these numerical forecasts, we could see two to three inches of rain in the Los Angeles area by Monday afternoon, and significantly more in orographically favored foothill and mountain locations. The NAM forecasts moist southerly winds approaching 60 kts at the 5000 ft. level Sunday evening.

BUFKIT analysis of 12z NAM/GFS data generates 2.16/4.11 inches of rain for LAX, 3.56/3.57 inches for Van Nuys, and 4.01/4.20 inches for Santa Barbara. The GFS brings in the second front faster than the NAM, forecasting the onset of heavier rain during the day Sunday, rather than Sunday evening. The 09z SREF puts the probability of more than 1.0 inch of rain in the Los Angeles area for the 24 hour period ending Monday morning at about 90%.

And yes, it does look like there's a chance of rain for the Los Angeles Marathon. Although the heavies rain is forecast to hold off until Sunday afternoon or evening, the 09z SREF pegs the probability of 0.1 inch of rain or more in the Los Angeles area over the 6 hours ending at 11:00 a.m. Sunday at about 70%. BUFKIT analysis of 12z NAM data generates about 0.20 inch at LAX from 8:00 a.m. to noon, with temps in the mid 50's. The GFS says about 0.50 inch over the same period. We'll see!

Be sure to check the NWS Los Angeles/Oxnard web site for the latest forecasts, advisories and warnings. More information about Southern California weather and climate can be found using our WEATHER LINKS page.