In a classic case of "be careful what you wish for," Southern California has been awash in a series of storms that rival those of the biggest El Nino years. Coming on top of the rain we've already recorded this week, today's and Thursday's systems appear likely to deliver a combination punch with potentially serious consequences.

Yesterday's vigorous system was characterized by scattered thunderstorms, heavy downpours, and damaging winds. Rainfall amounts generally ranged from about 0.5 inch to 1.0 inch, with some isolated higher amounts. Here's an archived copy of NWS Public Information Statement with preliminary rainfall totals for the period 5:00 a.m. to 4:00 p.m. Tuesday.

Today's frontal system, the fourth in the series since Sunday, is producing heavy rain, strong winds, and the possibility of thunderstorms. More rain is expected than resulted from yesterday's storm. BUFKIT analysis of 18z NAM data for Van Nuys (VNY) indicates about 2 inches of rain today and tonight, with generalized rain rates peaking at about 0.4 inch/hour. Higher localized rainfall rates could occur in the vicinity of thunderstorms. Here is an archived copy of a NWS Los Angeles Quantitative Precipitation Statement with more detailed information.

Unlike previous systems this week, Thursday's system is forecast to develop a surface low west of Pt. Conception. According to the WRF forecast a multi-centered surface low will develop and deepen into a 972 mb low west to northwest of Pt. Conception. In addition to the usual dynamics associated with such a low, a very strong jet is forecast to be in a position overhead that would maximize system dynamics. The formation of a surface low could also slow the progress of the system, potentially increasing precipitation totals.

Please refer to www.weather.gov/losangeles for the latest warnings and weather information.

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A potent appearing Pacific storm system is developing off the coast of Oregon and Northern California and headed our way. Significant rain, with snow at the higher elevations, is expected over much of the state.

Rain associated with this system is forecast to begin in Northern California this evening. At the moment, it looks like prefrontal rain could develop in the Los Angeles area tomorrow morning. Rainfall rates are forecast to increase Christmas Eve, and then taper off during the day on Christmas.

Although the models appear to be converging on similar solutions, there has been a lot of variability from run to run. This is due in part to the difficulty of the forecast. The intensity of the low, the path of the low center, the amount of moisture available to the system, the upper and lower level jet dynamics and other factors could change the amount of rainfall.

The HPC QPF forecast for the period Tuesday afternoon to Friday afternoon shows about 1.25 to 1.50 inches along the coast with up to about 3 inches in the mountains. These amounts could be somewhat understated. We'll see!

The system that moved through the Los Angeles area Sunday night into Monday was a little stronger than expected, with rainfall amounts generally ranging from about 0.1 inch to 0.25 inch. Here are some preliminary rainfall totals from the NWS.

Update 12/24/08 11:00 am. 12z NAM and GFS forecast a more westward track of the low and have backed off precipitation amounts forecast for the Los Angeles area. The 12z NAM generates about 0.6 inch at Van Nuys and the 12z GFS only about 0.26 inch for the storm. HPC's latest 2-day Quantitative Precipitation Forecast indicates precipitation amounts ranging from about 0.75 inch to 1.50 inch in coastal Southern California. On the other hand, the 06z high resolution WRF-NMM was quite wet, with precipitation amounts in our area ranging from 1.0 to 4.0 inches.

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It's been a couple of weeks since an upper level low set rainfall records for the date at several Southern California locations, and pushed water year rainfall totals above normal at Los Angeles. Since then we've had almost no rain, and as of yesterday, Downtown Los Angeles (USC) rainfall has dropped to about six-tenths of an inch below normal. If a storm later this weekend works out as expected, we could be back above normal by Monday night.

Several factors could affect the forecast. As we've seen earlier this season, the computer models don't do a particularly good job with high amplitude flows, retrograding ridges and digging troughs. Throw into the mix a strong 150-170 kt. jet stream, sub-tropical moisture being advected from Hawaii (nearly) to the Aleutians, and cold air being drawn down from Canada and Alaska, and there is the potential for high impact weather.

A chance of showers is forecast Saturday into Sunday, but at the moment, the main event is forecast for Sunday evening through Monday. HPC's QPF for that period indicates rainfall amounts ranging from about 0.75 inch to 2 inches or more in the mountains. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.