California snow: atmospheric Category 3 river will deliver feet of snow

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“This is a successful winter storm event for us,” said Mark Deutschendorf, meteorologist with the National Weather Service in Reno, Nevada. “It is not recommended to travel Tuesday night through Friday in the Sierra and Lake Tahoe area, including western Nevada. If you are venturing outside, be prepared to spend extended time in your car. ”

This is just another example of California stuck in a “weather boost” – moving from one weather extreme to the opposite extreme.

A dramatic change in landscape will occur as winter shifts into high gear.

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

The foothills could see 6 inches to a foot of snow while the mountains could see 3 to 5 feet. In some areas, up to 7 feet are expected on prime Sierra Nevada terrain until Friday.

“This storm remains projected to be a major headache for the region and will bring heavy snowfall to the Sierra as well as parts of western Nevada,” NWS Reno said.
An avalanche watch in the hinterland is in effect for much of the region, including the Tahoe Basin, until Friday. The combination of heavy snowfall and strong winds will result in extreme avalanche danger, according to the NWS.

Ridgetops in the Sierra could see gusts exceeding 125 mph.

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

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

The moisture laden air from this Atmospheric River Event (RA) will be forced to rise above the crest of the mountains and rise upward, cooling as it rises. As the air cools, it condenses, forming heavy precipitation, which will flirt with record snowfall duration.

“The Owens Valley (Great Basin Desert) could receive near-record amounts of snow over a two-day period. Their previous record for 48-hour snowfall was 23 inches in 1969,” the meteorologist said. NWS Jenn Varian at CNN.

Atmospheric river creates flash flood potential

As the atmospheric river points its lance along the central coast, total excessive precipitation of 4 to 8 inches will threaten flash floods in the region.

San Francisco averages 4.19 inches of rain in January. Suppose that the atmospheric river concentrates the heaviest rainfall in the bay area: in this case, it is possible that the city will receive a month’s rainfall in just a few days.

Depending on the precise location of the atmospheric river, coastal areas south of San Francisco to Santa Barbara could receive between 5 and 10 inches of rain with locally higher amounts. Lesser but still significant rainfall totals of 1 to 2 inches are likely from Los Angeles to San Diego.

Evacuations in progress as the risk of debris flow increases

This heavy rainfall combined with the scars of burns from the record-breaking wildfire season of 2020 present a dangerous risk of mudslides and debris flows.
Forecasters are particularly concerned about Monterey County and Santa Cruz County where evacuations are underway, according to a statement issued by the California Department of Forestry and Fire Protection.

Intense forest fires can compromise soil structure, making sloping land more vulnerable to debris flows and landslides during heavy rains.

If enough rain falls on a recent burn scar, a torrent of mud, rocks and debris can cascade down and put communities at risk. Properties directly affected by recent fires or those located directly downstream of burn areas are most at risk.

Storms could ease current drought conditions

Although atmospheric rivers can be dangerous, residents rely on them to bring beneficial precipitation to the area.

“Thirty to 50 percent of annual precipitation on the West Coast occurs in just a few AR events,” according to NOAA.

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

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

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

Severe drought conditions cover nearly 80% of California.

However, like everything in moderation, it is possible to have too many good things.

This ‘weather boost’ will happen more often

Research shows that the west coast of the United States, especially California, can expect more climate extremes in the future.
Extreme precipitation – such as the current atmospheric river – will intensify while periods of drought are likely to become longer and more frequent, climatologists say.
“In a country like California, we really have to think about the two risks [drought and flood] simultaneously, ”said Daniel Swain, climatologist at the University of California at Los Angeles and lead author of a study on the subject.
Drastic changes from very wet to extremely dry and vice versa will be almost twice as likely, occurring on average once every 25 years, by 2100.
According to a study published in the journal Nature Climate Change, dramatic fluctuations are becoming more common and will continue to do so in the decades to come thanks to human-caused climate change.

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

The variability of the climate is in part due to human activity such as the combustion of fossil fuels.



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