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California Atmospheric River to Bring Threat of Flooding, Debris Flows and Feet of Sierra Snow
Weather.com
By Chris Dolceless than an hour ago
An atmospheric river is poised to take aim at California beginning late Tuesday with drenching rains that could trigger debris flows and flooding while feet of snow pile up in the Sierra Nevada.
A pattern change late last week opened the door for an active storm track to bring much-needed rain and mountain snowfall to California and other parts of the Southwest. Two weather systems have impacted the region over the last few days, but neither produced widespread, heavy rainfall given their cold origin from the North Pacific.
That will change by late Tuesday into Wednesday when a new low-pressure system approaches the Golden State. What this storm will have that its predecessors did not is a thin, long plume of moisture in the atmosphere that stretches from the Pacific Ocean subtropics called an atmospheric river.
These plumes of moisture can bring heavier rainfall when they set up in California's wet season from late fall through early spring, and that's what we expect to happen this week. You can see the ribbon of moisture approaching the West Coast in the dark green and yellow shadings in the map below.
While California needs rain and snowpack to combat an ongoing drought in much of the state, this could be a case of too much of a good thing. That's because the heavy rain might contribute to flooding and debris flows in parts of the state this week.
Recent burn areas from the record-breaking 2020 wildfires in California are of greatest concern at this time. However, some flooding and debris flows could occur outside these charred areas.
Here's what to expect.
Forecast
Flood Threat
The greatest rainfall totals from this event will be in coastal parts of Northern and Central California, which is where the atmospheric river moisture plume is expected to be most persistent late Tuesday through Thursday. This includes locations from around the Bay Area southward to Big Sur and parts of San Luis Obispo and Santa Barbara counties.
Rainfall totals in elevated locations along this stretch of the coast could be 5 to 8 inches (locally higher). Lower elevations may pick up 3 or more inches of rain.
A pattern change late last week opened the door for an active storm track to bring much-needed rain and mountain snowfall to California and other parts of the Southwest. Two weather systems have impacted the region over the last few days, but neither produced widespread, heavy rainfall given their cold origin from the North Pacific.
That will change by late Tuesday into Wednesday when a new low-pressure system approaches the Golden State. What this storm will have that its predecessors did not is a thin, long plume of moisture in the atmosphere that stretches from the Pacific Ocean subtropics called an atmospheric river.
These plumes of moisture can bring heavier rainfall when they set up in California's wet season from late fall through early spring, and that's what we expect to happen this week. You can see the ribbon of moisture approaching the West Coast in the dark green and yellow shadings in the map below.
While California needs rain and snowpack to combat an ongoing drought in much of the state, this could be a case of too much of a good thing. That's because the heavy rain might contribute to flooding and debris flows in parts of the state this week.
Recent burn areas from the record-breaking 2020 wildfires in California are of greatest concern at this time. However, some flooding and debris flows could occur outside these charred areas.
Here's what to expect.
Forecast
Flood Threat
The greatest rainfall totals from this event will be in coastal parts of Northern and Central California, which is where the atmospheric river moisture plume is expected to be most persistent late Tuesday through Thursday. This includes locations from around the Bay Area southward to Big Sur and parts of San Luis Obispo and Santa Barbara counties.
Rainfall totals in elevated locations along this stretch of the coast could be 5 to 8 inches (locally higher). Lower elevations may pick up 3 or more inches of rain.
More, including maps: https://weather.com/forecast/regional/news/2021-01-25-california-forecast-atmospheric-river-debris-flows-flooding-snow
This seems pretty important, so I'm posting two stories about it.
Be safe!
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