Strong storm to drench California, raise flooding risk

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The strongest storm so far this season and perhaps in several years for California will bring drenching rain to hard-hit drought areas, along with the risk of damaging winds, flooding and mudslides la

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The strongest storm so far this season and perhaps in several years for California will bring drenching rain to hard-hit drought areas, along with the risk of damaging winds, flooding and mudslides later this week.

The train of December storms will continue to roll along over the Pacific Ocean and into the West Coast of the United States this week.

Rainfall from this single storm could approach the average rainfall for the entire month December in some areas. In some cases, this has the potential to be biggest single rain-producer about 10 years.

The most potent storm in the train will deliver millions of gallons of water per square mile on much of California during the second half of this week.

Storm to Attack Drought

From 1-3 inches of rain will fall on coastal Southern California with an average of 3-6 inches of rain forecast over central and northern parts of the state. This translates to between 17 and 100 million gallons per square mile from this storm alone.

Locally higher amounts of rain, up to a foot, are possible on some of the west- and southwest-facing slopes of the coastal ranges, Sierra Nevada and southern Cascades.

While more rain than what this storm will deliver will be needed to end the drought completely, this will be a major step in the right direction. The ground will be thoroughly soaked.

Runoff from the storm will cause water levels to surge rapidly in streams and will eventually begin to empty into lakes and reservoirs.

Travel Disruptions and Risks to Property Owners

In addition to the positive impact the storm will bring, it will also cause adverse conditions.

Disruptions to travel and outdoor activities will be the biggest negative from the storm, impacting millions. The storm will cause flooding in poor drainage areas and will result in poor visibility for drivers along Interstate-5 and other major routes.

The heavy rain will be of concern for some motorists and property owners. Mudslides and rock slides are likely. The risk of mudslides will be greatest in recent burn areas.

Enough rain can fall to lead to stream flooding and high water on some of the rivers. Normally dry washes over the deserts could be subject to flash flooding.

Snow levels will drop below Donner Pass at 7,200 feet on I-80 in the Sierra Nevada.
According to Western Weather Expert Ken Clark, “A foot of snow could fall at an elevation around 6,000 feet with 2 feet of snow or more possible above 7,000 feet.”

Snow falling at the rate of several inches per hour can lead to whiteout conditions.
Low cloud ceilings and gusty winds may cause flight delays.

Wind gusts can be strong enough along the coast and over the hills and mountains to down trees and cause sporadic power outages. Gusts to 60 mph are possible along the central and northern California coast, over the ridges and through the passes.

Wind-driven waves will batter coastal areas, especially in central and northern areas of California. Offshore waves and swells will approach 20 feet with the storm.

Biggest Storm in Nearly 10 Years for Northern California

For Sacramento, California, this storm has the potential to bring between 3 and 6 inches of rain over a span of two to three days. During December 2005 to the first couple of days of January 2006, 10.52 inches of rain fell with 4.57 inches of rain falling from Dec. 30, 2005, to Jan. 2, 2006.

At San Francisco, 9.34 inches of rain fell during December 2005, compared to an average of 4.03 inches for the month. So far this month, close to 4 inches of rain has fallen with the potential to double that amount in the wake of the Wednesday night to Friday storm.

Rainfall from this storm will be heavy in parts of southern California, but it will be unlikely to exceed that of the storms during December 2010. During December 2010, 8.83 inches of rain fell at Los Angeles, which was more than four times that of average for the month. So far this month, Los Angeles has received 1.33 inches of rain.

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About the author


Editor in chief is Linda Hohnholz.