Snow in California: A Category 3 atmospheric river provides meters of snow

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“This is a tremendous winter storm for us,” said Mark Deutschendorf, a meteorologist with the National Weather Service in Reno, Nevada. “Traveling is not recommended Tuesday night through Friday through the Sierra and Lake Tahoe, including western Nevada. If you do go outside, be prepared to spend longer in your car.”

This is just another example of California stuck in “weather whiplash” – going from one extreme weather to another extreme.

A dramatic shift in the landscape will occur as winter picks up a gear.

“Parts of the Sierra need a yardstick to measure the snow forecast in the forecast,” the tweeted NWS in Sacramento Monday.

The foothills could see 6 inches to 12 inches of snow, while the mountains could see 1 to 1 meter long. In some areas, up to 7 feet is forecast over the Sierra Nevada’s favored terrain through Friday.

“This storm is expected to remain a major headache for the region and will cause heavy snow in the Sierra and parts of western Nevada,” said NWS Reno.
An avalanche watch in the interior applies to much of the region, including the Tahoe Basin, through Friday. The combination of heavy snowfall and high winds will create extreme avalanche danger, according to the NWS.

Ridgetops in the Sierra could see gusts of wind in excess of 200 mph.

This heavy snowfall is all due to a category 3 – out of 5 – atmospheric river.

Atmospheric rivers are long, narrow areas of the atmosphere – like rivers in the air – that carry water vapor, according to the National Oceanic and Atmospheric Administration.

The moisture-laden air from this atmospheric river event (AR) will be forced to rise over the top of the mountains and rise upward as it cools. As the air cools, it condenses to form heavy precipitation, which will flirt with snowfall duration records.

“The Owens Valley (Great Basin Desert) could receive nearly record amounts of snow over a two-day period. Their previous record of 48 hours of snowfall was 23 inches back in 1969,” NWS Meteorologist Jenn Varian told CNN.

Atmospheric river creates potential for flash flooding

As the atmospheric river directs its fire hose along the central coast, excessive rainfall of 10 to 20 cm threatens flash flooding in the region.

San Francisco has an average of 4.19 inches of rain in January. Suppose the atmospheric river concentrates the heaviest rainfall in the Bay Area: in that case, the city could get a month’s worth of rainfall in a few days.

Depending on the precise placement of the atmospheric river, coastal locations south of San Francisco to Santa Barbara can receive between 5 and 10 inches of rain with higher amounts locally. Smaller but still significant 1 to 2 inch rain totals are likely from Los Angeles to San Diego.

Evacuations in progress as the risk of debris flows increases

This torrential rainfall coupled with the burn scars from the record wildfire season of 2020 poses a dangerous risk of mudslides and debris slides.
According to a statement by the California Department of Forestry and Fire Protection, forecasters are particularly concerned about Monterey County and Santa Cruz County, where evacuations are taking place.

Intense forest fires can affect soil structure, making sloping terrain more vulnerable to debris and mudslides during heavy downpours.

If enough rain falls on a recent burn scar, a torrent of mud, rocks and debris can spill downhill and endanger communities. Properties directly affected by recent fires or located directly downstream from combustion areas are most at risk.

The storms could ease the current drought

While atmospheric rivers can be dangerous, residents rely on them to bring favorable rainfall to the region.

“Thirty to 50 percent of the West Coast’s annual rainfall occurs in just a few AR events,” said NOAA.

California’s wintry snowpack, fed in part by atmospheric rivers, is critical to the state’s water supply. Warmer spring temperatures melt the snow and fill the reservoirs, so fresh water is available during the drier summer months.

This AR event can be considered a much needed relief as the current statewide snowpack is only 40% of the average to date.

This storm, along with an active weather pattern forecast in early February, will help ease droughts in California and the Great Basin.

Nearly 80% of California is in severe drought.

However, like anything in moderation, it is possible to have too much of a good thing.

This ‘weather whiplash’ will occur more often

Research shows that the US west coast, especially California, can expect more climate extremes in the future.
Precipitation extremes – such as today’s atmospheric river – will increase, while dry spells are likely to become longer and more frequent, according to climate scientists.
“In a place like California, we really need to think about both risks [drought and flood] at the same time, ”said Daniel Swain, climate scientist at the University of California, Los Angeles and lead author of a study on the topic.
Drastic swings from extremely wet to extremely dry and vice versa will be nearly twice as likely, once every 25 years on average, by 2100.
Dramatic swings are increasingly common and will continue to do so for decades to come thanks to man-made climate change, according to a study published in the journal Nature Climate Change.

Drastic swings from extremely wet to extremely dry and vice versa will be nearly twice as likely, once every 25 years on average, by 2100.

Climate variability is due in part to human activities, such as the burning of fossil fuels.

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