The strongest storm so far this season and in the last four to 10 years for California continues to deliver drenching rain to hard-hit drought areas, along with the risk of damaging winds, flooding and mudslides.
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 persist through Friday, impacting millions. The storm will cause more 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. Additional mudslides and rock slides are likely in Southern California through Friday. The risk of mudslides will be greatest in recent burn areas.
A major mud and debris flow occurred early Friday morning in Camarillo Springs, in the Springs burn area. The debris flow affected several homes on San Como Lane, according to the Los Angeles NWS Office.
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.
Snow levels will not dip down to Tejon and Cajon passes, but fog and heavy rain will be a problem.
Low cloud ceilings and gusty winds may cause flight delays.
The gusts can make travel dangerous for high profile vehicles on the bridges and could lead to lengthy flight delays at area airports.
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 a total of between 3 and 6 inches of rain. 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. 12, 2014, over 7 inches of rain fell this month, half of which fell during this event.
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 12, Los Angeles had received 2.14 inches of rain.