After nearly two weeks of idyllic days with temps in the 70's and 80's, it rained in Southern California last night and into this morning. But today's rain is just a precursor. Just a little reminder that it's the rainy season in Southern California, and more rain is on the way -- possibly a lot more rain.

Skies will start to clear later today, and temps are forecast to be back into the 70's tomorrow. But the dry weather won't last. For several days forecast tools have been projecting a major pattern change -- to a wet pattern more like what might be expected in January of an El Nino year.

Today's Climate Prediction Center 6-10 day precipitation outlook indicates a 70% probability that precipitation will be above normal in Southern California for the period January 19-23, and the 8-14 day precipitation outlook indicates a 60% probability that precipitation will be above normal for the period January 21-27.

As part of its analysis, the CPC now uses historical analogs with 500 hPa patterns similar to the current forecast. In the 6-10 day forecast period the 10 most similar analogs produced above average precipitation in Southern California 9 out of 10 times. In the 8-14 day period the 10 closest analogs produced above average precipitation 6 or 7 times out of 10. Also of note, many of the analog cases with the most similar 500 hPa patterns are from wet El Nino years, such as 1958, 1978, 1983, 1992, 1995, and 1998.

Late in the weekend, around Sunday evening, the first of these potentially strong systems is expected to move onshore. Additional impulses and systems are forecast to follow in quick succession, driven by a fast moving zonal flow and strong jet stream. If current computer projections validate, the wet pattern could continue through the end of January. If precipitation totals approach what is forecast over the period, a host of rain related impacts are a possibility. We'll see.

Update January 15, 2010. PDF of slides from NWS Los Angeles/Oxnard Weather Briefing "Significant Storm Impacts For Southern California Next Week" by Eric Boldt Warning Coordination Meteorologist. Presented on January 14, 2010. Please refer to www.weather.gov/losangeles for the latest information.

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Related post: How Does the El Nino of 2009-10 Compare to Other Warm ENSO Episodes Since 1950?