Major storm threatens flooding, heavy snow across California this week

Meteorologists say a colossal storm could impact every region of the country, first rolling ashore along the Pacific Coast on Wednesday, bringing soaking rain and heavy snow to California and other western states as it moves inland. The National Weather Service in Los Angeles warned of rock and mudslides.

An inch of snow could fall at California elevations as low as 3,000 feet, with 1 to 5 inches possible between 4,000 to 5,500 feet. Some snow could even fall as low as 2,500 feet, said Rose Schoenfeld, a meteorologist with the National Weather Service in Oxnard.

That snowfall could impact travel over the Grapevine section of Interstate 5 starting Wednesday night through Friday morning. The mountainous corridor passes over Tejon Pass at around 4,144 feet.

Over the next week, tens of millions of Americans will be at risk of severe weather as the storm marches across the country, threatening hurricane-force winds, major flooding, blizzard conditions and a possible tornado outbreak.

By Friday, the massive storm will stretch across nearly the entire central U.S., from the Gulf Coast to the Canadian border, threatening everything from whiteout conditions to damaging winds, unusually warm temperatures, wildfires, dust storms and tornadoes.

AccuWeather senior meteorologist Tom Kines told USA TODAY the storm could be among the strongest on record in terms of low pressure.

"This is going to be a very significant, very strong storm," he said, adding that the barrage of extreme weather will likely lead to power outages and travel delays on roads and at airports.

West Coast braces for deluge, snowstorms

The National Weather Service says the storm will arrive on the West Coast early Wednesday and bring heavy rain to coastal California.

Southern California is at risk of flash flooding and debris flow, the weather service said, especially in areas impacted by the outbreak of wildfires in January. San Francisco could also see heavy rain on Wednesday.

As the storm heads east, it is expected to blanket the Sierra Nevada mountains in 2 to 4 feet of snow and produce widespread wind gusts of 40 to 70 mph, Kines said.

From Thursday into Friday, snow will bury parts of the Rockies and stretch into Nevada, Utah and Arizona, which has seen less snow this winter than usual. From Friday into the weekend, much of the Plains region will be at risk of heavy snow and possible blizzard conditions as the low-pressure system strengthens, the Weather Prediction Center said.

While these conditions could lead to travel delays and treacherous road conditions, they will also bring much needed moisture to the region. "More storms with generous rain and mountain snow are needed prior to the beginning of the dry season, less than a couple of months away," said AccuWeather senior meteorologist Alex Sosnowski in an online forecast.

Ernesto Centeno Araujo of the Ventura County Star contributed to this report.