Barrage of storms to aim for West Coast through early January

As the Northwestern states continue to get pummeled with rain and feet of snow, forecasters say that a slight southward dip in the storm track this week will bring much-needed precipitation to California, where the rainy season has been off to a slow start.

Over the coming week, portions of Northern California have the potential to receive nearly as much precipitation as they did during the entire month of December. During last month, rainfall was less than half of average in places such as Eureka, Redding, Sacramento and San Francisco.

It was a different story farther north, however, as Seattle and Portland, Oregon, started off the rainy season at a fairly average pace.

"So far, since a La Niña pattern has set up, significant amounts of rainfall and, at higher elevations, snowfall have been observed through the season so far in the Northwest," AccuWeather Lead Long-Range Meteorologist Paul Pastelok explained.

"This pattern will continue through the first week of January with several waves of moisture arriving in the Pacific Northwest," Pastelok said.

A new weather system is likely to arrive on the coast every one to two days through the week.

One such storm swept through the Northwest over the weekend with soaking rain, mountain snow, high winds and pounding surf. On Saturday night, this storm created slippery, snow-covered roadways that stranded motorists and forced the closure of a 75-mile stretch of Interstate 90 in Washington.

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There was only a brief break in precipitation during the day on Sunday before the next storm came knocking on the doorstep at night. This storm will plow inland into Monday night, before targeting the Rockies and northern Plains with snow Tuesday into Wednesday.

This early week storm had dipped far enough to the south to bring a beneficial soaking rain to the Bay Area while heavy snow over the high country of the Sierra Nevada.

In the Sacramento Valley, a short-lived storm spun up a tornado that touched down near Molinos, California, becoming the first twister of 2021 west of the Mississippi River. No damage was reported.

"Snow levels are forecast to dip enough over the Sierra Nevada to bring several hours and several inches of snow to Donner Pass, California into Monday evening," according to AccuWeather Senior Meteorologist Alex Sosnowski.

Motorists should be prepared for delays and slippery travel as a result.

Snow tires and chains may be required, with lane restrictions also possible. Motorists venturing over the passes through the Cascades should also be ready for winter weather hazards.

"Although this isn't the first blast of rain and snow across California for the season, the region is still desperately moisture starved given a very late onset of the rainy season and an exceptionally dry year prior to late December," Pastelok said.

Most of California remains in severe to extreme drought as a result of a dry 2020.

As some residents return to normal routines this week, the I-5 corridor from Seattle to Sacramento is likely to be a slow-go with reduced visibility from downpours as well as ponding of the water on the roadway. Shower activity may extend as far to the south as Fresno, California, into Monday night.

Unlike a storm this past week that brought a rare snowfall to Southern California, rain is unlikely to reach places such as Los Angeles and San Diego.

Strong winds will whip along the coasts of Washington, Oregon and Northern California as the storm comes ashore, with gusts past 60 mph possible. Such winds can lead to an increased threat of fallen trees and downed power lines due to the saturated, unstable nature of the ground.

As this storm moves inland on Tuesday and spreads snow through the Rockies, another plume of moisture will be knocking on the door of the West coast, poised to spread inland by midweek.

With each subsequent storm over the course of the week, the risk for flash flooding will increase as the ground becomes increasingly saturated and unable to absorb as much water. Anyone living downhill of burn scars will need to be wary of the threat for mudslides as well.

At the very least, the stormy pattern is likely to increase travel disruptions and make it difficult for residents to find extended dry periods to get outside.

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