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An atmospheric river is forecast to deliver up to a foot of rain and feet of snow to California

<i>CNN Weather</i><br/>Warmer temperatures are gripping the eastern half of the country.
CNN Weather
Warmer temperatures are gripping the eastern half of the country.

By Judson Jones, CNN Meteorologist

As people continue picking up the pieces from this weekend’s deadly tornado outbreak, a new storm system is intensifying. This one is out West.

An atmospheric river — a plume of moisture, similar to a river, that streams in off the Pacific Ocean and brings extreme rains — is unleashing flooding rainfall of up to a foot and several feet of snow on the West Coast.

The storm began in Washington this weekend, where it created unstable conditions and led to at least one avalanche in the region. Now it’s meandering down the coast, first soaking people in the Bay area Sunday and now unleashing extreme rainfall on the central California coast.

San Francisco has already received more than 2 inches of rain with this system.

“Models indicate that an atmospheric river event will intensify through the early morning hours, resulting in heavy rainfall,” the Weather Predictions Center said.

It appears the steadiest and highest rainfall rates will be concentrated along the Big Sur coast through the afternoon and evening hours, according to the National Weather Service office in San Francisco.

“Isolated amounts of 10-12 inches are possible for the higher peaks,” the San Francisco office said.

A Level 3 of 4 threat for extreme rainfall is in place for this region Monday. The system will continue its move down the coast Monday night.

“All systems go for a strong and impactful storm to move into southwest California later tonight and hang around through Tuesday,” said the weather office in Los Angeles, adding it expects 2 to 3 times more rainfall than an October storm that struck the region.

This storm could end up dropping 2 to 3 inches of rain downtown, the most rainfall the city has seen for about a year. The last time the office recorded a storm total over an inch was in January.

“Heavy mountain snow and lowland rain will overspread California and the Great Basin today and Tuesday,” the WPC tweeted. “Heavy snow is likely across much of the terrain, accumulating to 6 feet or more in parts of the Sierra Nevada. Mountain travel may become impossible.”

Mount Shasta was already reporting more than a foot of snow Monday morning.

Snow in the Sierra could fall at rates of 3 inches an hour or greater at times this evening into early Tuesday. This extreme snow, combined with strong winds — gusts of between 40 to 60 mph and 100 to 120 mph for exposed Sierra ridges — will produce whiteout conditions and potential highway closures, the Reno, Nevada, weather service office said.

Wind advisories are in effect for large portions of California, western Arizona, Nevada, southern Oregon, southwestern Idaho. High wind warnings are in effect for the Southern Coast Ranges, Transverse Ranges, and Peninsular Ranges of California, the Sierra Nevada of Nevada, and the Wyoming Basin.

The Reno office adds some of these heavy snow bands could be intense enough to create thundersnow.

“The heavy snow will be a long-duration event over the Cascades, Sierra Nevada Mountains, and Northern Rockies,” the Weather Prediction Center said.

The snow won’t just be for the higher elevations. The Pacific Northwest and Northern California will see colder air moving in over the next day.

“The snow levels will drop down to sea level over parts of the Pacific Northwest and down to the surface over parts of Northern California overnight Monday into Tuesday morning,” the prediction center said.

The energy from this system ultimately will move into the central US later in the week, threatening to bring rain to the areas recently hit by the devastating tornadoes.

Deadly nocturnal tornadoes

Tales of survival and heroics are emerging from the rubble of this weekend’s deadly tornadoes.

“It happened so fast,” Kyanna Parsons-Perez told CNN, describing the onslaught of destruction after a tornado struck a Mayfield, Kentucky, candle factory. “We all just rocked back and forth, and then boom, everything fell on us.”

You can read more of her story and others here.

CNN weather’s special newsletter over this past weekend mentioned this storm could result in one of the longest — if not the longest — tornado paths ever.

You can read an update about those potential records here.

The National Weather Service will continue to survey the damage today and over the following days. You can stay up to date with our live coverage here.

Most importantly, here is how you can help victims of this tragedy.

A December swelter

Warmer temperatures are gripping the eastern half of the country. It may, in fact, feel more a like ‘swelter weather’ instead of ‘sweater weather’ in some places in the central US. High temperatures may soar as high as 20 to 40 degrees above average Tuesday and Wednesday afternoon. Many temperature records are expected to be broken across the Plains.

Temperatures cool back down in the central US on Thursday as the storm system out West pushes through and milder weather slides into the East Coast.

Those milder temps might make it more enjoyable to go stargazing this week.

One of the best showers of the year

If you are up for staying up all night, the Geminids will light up the night sky Monday night into Tuesday morning.

NASA calls this meteor shower “one of the best and most reliable” for its bright, fast and abundant meteors.

Read more

Your chances of a white Christmas

Don’t blame the meteorologist. Blame the Grinch also known as climate change, but the probability of a white Christmas has gone down for many.

Use our interactive map to check the probability for your location here.

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