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Firehose of Pacific Moisture Takes Aim at W. Coast
October 25, 2021
UPDATED By WeatherBug Meteorologists
A potent weather system and an “atmospheric river” will bring everything but the kitchen sink to the western U.S. into the start of the new work week. Heavy rain, mountain snow measured in feet not inches, high winds and concerns for flooding and landslides will all be possible.
An unseasonably strong upper-level weather system will continue to strengthen and expand farther east and south into California, the northern Rockies and the Great Basin today. This system will also be associated with an “atmospheric river,” which is a plume of moisture that stretches across the eastern Pacific. When there is an atmospheric river pattern, a tremendous amount of moisture is pointed directly into parts of the West Coast.
This Pacific moisture will be aimed directly towards northern and central California today. Storm total rainfall of 2 to 5 inches will be common across the San Francisco Bay Area and San Joaquin Valley, with 5 to 10 inches Sacramento Valley. Portions of the western Sierra Nevada foothills could even pick up as much as 15 inches of rain when all is said and done!
The rest of the West Coast will also be in for some much-needed rain, though amounts won’t be as high as they are in northern California. Western Washington and Oregon could pick up 1 to 3 inches of rain by this evening, with some locally higher amounts up to 4 inches. The rest of Washington and Oregon will likely measure one-half inch up to 2 inches of rain. Los Angeles and San Diego could see some rain as well, but the moisture finally runs out by the time it reaches the Mojave Desert.
Flash Flood Watches and Flood Warnings are in place today mainly across the interior parts of northern and central California. This includes the burn areas near Lake Tahoe, and in Kings Canyon and Sequoia National Park.
At the same time, colder air will be invading the region, sending snow levels plummeting to around 6,000 feet. Once the rain changes to snow, it will accumulate rather quickly! While Truckee and Mammoth Lakes, Calif., and the Tahoe Basin will likely only see a few inches, snowfall accumulations of 6 to 18 inches of will be possible across the mountain passes to get to these locations, including Donner Pass, Echo Summit, Spooner Summit and Mt. Rose Summit. For the highest elevations of the Sierra Nevada, 2 to 4 feet of fresh powder will likely accumulate by the end of tofay.
Winter Storm Warnings are in effect across the entire length of the Sierra Nevada above the 6,000-to-9,000-foot level.
As if that weren’t enough, strong winds will be found across a good chunk of the western U.S. High Wind Warnings and Winds Advisories are scattered throughout Washington, Oregon, central Montana, southwestern Idaho, western North Dakota, Wyoming, California, Nevada, western Utah and northwestern Arizona . The strongest winds will occur over mountains and higher elevations, with sustained winds of 30 to 45 mph and wind gusts of 60 to 80 mph. This would include Walla Walla, Wash., Pendleton, Ore., Reno, Nev., and Salt Lake City. Other places like Portland, Ore., San Francisco, Sacramento and Modesto, Calif., and Boise, Idaho, are at risk for wind gusts of 40 to 50 mph.
This large weather system will slide into the Rockies by Tuesday and then the nation’s midsection on Wednesday. It will start to lose its moisture content as it gets cut-off from the “atmospheric river.” However, it will still provide several inches of snow to the Rockies and then some drenching rain in the Plains.
Heavy snow and high winds could potentially trigger power outages and long periods stuck in the house. It is important to have an emergency kit prepared should you be stranded for an unseeable amount of time. A simple kit comprised of non-perishable food items, blankets, water, batteries, and a radio could go a long way in remaining safe when calamity strikes. Remember to download the WeatherBug app to stay up to date on the latest.