WeatherFanatics: Biggest Storm in Years for California to Cause Flooding, Mudslides

Thursday, December 11, 2014

Biggest Storm in Years for California to Cause Flooding, Mudslides

By Alex Sosnowski, Expert Senior Meteorologist

December 11,2014; 9:52PM,EST

The strongest storm so far this season and in the last four to 10 years for California will bring drenching rain to hard-hit drought areas, along with the risk of damaging winds, flooding and mudslides during the second half of 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 of 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 through Friday.
"There is plenty of moisture for this storm to tap," said AccuWeather.com Western Weather Expert Ken Clark. "And this is why it will be such a soaking rain."

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.
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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 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 from western Washington state to central California.
The gusts can make travel dangerous for high profile vehicles on the bridges and could lead to lengthy flight delays at area airports.

Many locations along the coast, over the ridges and through the passes will experience gusts between 50 and 70 mph.
"Strong winds aloft, combined with the approach of a strong cold front will translate to winds to well over 100 mph on the Sierra ridges into Thursday with local gusts to 130 mph," Clark said.
Wind-driven waves will batter coastal areas, especially in Oregon and central and northern areas of California. Offshore waves and swells will approach 20 feet with the storm.
Biggest Storm in Years for California
Multiple big storms have hit California in the past decade. In some locations the storm this week will bring the most rain from a single system in about 10 years.
For northern areas the storm this week will rival that of the past four to 10 years. Some storms of note in the north occurred in February 2009, October 2009 and a day or two either side of the start of the new year in January 2006. In Southern California, the recent benchmark is most likely during December 2010.
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. As of Dec. 10, 2014, close to 4 inches of rain fell this month 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. As of the December 10, Los Angeles had received 1.33 inches of rain.

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