Ken Clark

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One More Big Wallop

December 21, 2010; 2:16 PM ET

The epic storm continues in portions of the West, but at least now the tail end is in sight. However until that tail moves though, there is going to be a lot more weather and a lot more weather problems to deal with.

First, a satellite picture:

On this you can still see the subtropical plume of moisture over southernmost California that extends northeast into Utah. It is within that zone the heaviest rain has fallen today. This has been especially true in parts of Southern California from Los Angeles County to the Inland Empire and south to San Diego County. In the past 24 hours, there has been almost 10 inches of rain in the mountains of the eastern San Gabriels. Lytle Creek now has a storm total closing in on 20 inches since last Friday. Flood warnings are in effect for a number of streams and rivers. A serious situation came up today in southwestern Utah. As of mid-afternoon, the Trees Ranch Dam in Washington County is in danger of imminent failure. If a catastrophic failure takes place, over 50,000 cfs of water could rush toward the town of Rockville. Other flood warnings are in effect for southwestern Utah.

Off the coast of California, you can see the typical signature of a digging, cold trough. This is the caboose storm that will move through California over the next 24 hours, and into the southern Great Basin for Thursday. Rain across Southern California and the northeast will continue tonight and tomorrow, heavy at times, bringing additional flooding problems. There has been a lull in the precipitation today in central California, but that will be ending as rain increases in coverage an intensity later tonight. A cold front will move through central and Southern California tomorrow from west to east. With, and behind, that front can be a few thunderstorms with very heavy downpours, strong winds, and hail.

Additional rainfall in central California will be 0.50 to 1.50 inches, but with up to 3 inches in upslope areas. In Southern California 1.50 to 3.00 inches are likely from Los Angeles County on north, with 2 to 5 additional inches to the south and east. However in upslope areas of the south-facing mountains, additional rainfall could reach 4 to 9 inches.

Across the deserts of Southern California northeastward into southern Nevada and northeastward into Utah, the rain will be heavy at times through tomorrow and bring additional serious flooding problems. Also, a band of moderate to heavy rain will start to spread from west to east across Arizona Wednesday and Wednesday night. This can cause some flash flooding problems in Arizona.

As for snow, levels are lower than they have been in California. They should stay around 3,500 feet in the northern Sierra to 5,000 feet in the southern Sierra tonight, and around 6,000 feet in Southern California. Those snow levels will drop somewhat tomorrow, especially in central and southern areas. This means that the Southern California resorts will get some well-needed snow. Total additional accumulations will be 1 to 2 feet, with the highest amounts probable in the Mountain High area. There could be locally higher amounts. Farther east, snow levels will be higher initially, before falling. But substantial snow is likely in all the Utah and northern Arizona mountains.

When all is said and done, this storm will be one to remember. There are likely to be some areas in Southern California that will have received well over 2 feet of rain. Of course, there is all the snow that fell at Mammoth Mountain. Storm totals as of early today were as high as 15.5 feet, and they are likely to get another few feet of snow with this last storm moving through. Flooding problems will continue along some of the large rivers well past when the rain ends. A storm for the record books.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Ken Clark
Ken Clark's Western U.S. weather blog tackles daily weather events with commentary from one of the most experienced and trusted Western U.S. weather experts.