Atmospheric river sweeps down West Coast with flooding, mountain snow

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Some of the most drought-stricken areas on the West Coast are about to drenched in the next few days as several atmospheric rivers – tongues of deep tropical moisture originating in the central Pacific – rush in. .

Heavy rains bring much-needed rainfall to Washington, Oregon and parts of California. But these heavy rains also increase the risk of floods and landslides.

At higher elevations, the same system dumps several feet of snow. Parts of the Sierra Nevada range prepare for 3 to 5 feet more and can experience blizzard conditions on the highest peaks.

The next river in the atmospheric river conga line overlapped the Oregon coastline early Friday morning and was poised to drop in California. Flood monitoring covers much of the Golden State, including the central and northern San Joaquin Valley and coastal plains.

Warmth soars in eastern US — including places recovering from extreme cold

Wet conditions in many areas This week saturate the soil, Flooding is more likely.

“We’re definitely going to see wet soil,” said Andy Borenbacher, chief forecaster for the National Weather Service in Hanford, Calif. This created valleys of 1-2 inches in the foothills, 3-4 inches in the Sierra Nevada, and up to 5 inches in the mountains below the snowline. “

Flooding has been modest so far, but this could change during what is likely to be a busy travel period around New Year’s Eve.

“Soil doesn’t absorb as much water as it normally does,” he said. “It will cause nuisance flooding in areas with poor drainage and possibly some rockslides in the mountains. There is still water on the roads after Tuesday’s storm.”

About 1 to 2 inches of rain is likely in the San Joaquin Valley, atmospheric rivers are north of the Bay Area, and a small amount of rain, about 0.5 inches, is likely in the central and southern parts of the Central Valley. .

Atmospheric rivers carry most of their water a mile or more above the ground. Heavy rainfall is therefore usually confined to high altitudes. The Coastal Ranges can receive 2 to 4 inches of rain, and the Sierra Nevada Mountains can receive 3 to 7 inches of rain below the snowfall line.

San Francisco is 1.59 inches above average for the month to date, and Sacramento is about 1.65 inches above average.

Expect mostly snow above 7,000 feet. Typically 1 to 3 feet of snow is likely, with 3 feet or more above 8,000 feet and 5 feet or more above 9,000 feet.

Several cyclonic systems have caused atmospheric rivers. The first is the mature lowlands west of Vancouver Island, which, thanks to its counterclockwise rotation, draws the region’s moisture eastward from the tropical Pacific Ocean. That wet plume will be directed more directly into California on Saturday as a more intense storm develops west of the state and moves southeast.

Sliding past Nevada’s Great Basin on Sunday morning, we ring in the New Year in stormy conditions including heavy rain, 40- to 60-mph wind gusts, and mountain snow. Reno has flood watches and wind alerts.

Drought Increases Likelihood of ‘Doomsday Scenario’

The US Drought Monitor reports that 64% of the region is experiencing “moderate” or worse drought. In California, 7.16% of the state faces the highest level of “exceptional” drought. That’s a 4 out of 4 level, nine times more than the area affected this time last year.

Fortunately, a more atmospheric river is on the horizon, especially since Tuesday.

“In this case it looks like the jet pattern is much more [west to east]This suggests that the ‘Pineapple Express’, a moisture tap, is coming here more than in Oregon, Washington, or Western Canada. It looks like that for a few weeks, but it wasn’t this year.”

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