A strong atmospheric river moving inland Wednesday night through Friday will bring widespread rain, mountain snow, and gusty winds across California, with impacts spreading into Arizona, New Mexico, and Nevada over the weekend.
In Southern California, the system is expected to bring periods of rain, gusty winds, and mountain snow from Thursday night, Nov. 13, through the weekend. Some areas could experience locally heavy rainfall from Friday into Sunday, November 14–15, with the highest totals in the mountains.
Highs along the coast and in valley areas are expected to drop 5–10 degrees below normal by Friday, with desert highs dipping slightly below average. Snow levels will remain above 10,000 feet through Thursday, then drop to around 9,500 feet on Friday and approximately 7,500 feet on Saturday, primarily affecting higher mountain elevations.
Morning fog and low clouds may limit visibility in western valleys and near mesas, clearing during the day but returning overnight. Officials advise residents and travelers to monitor road conditions, especially in desert washes and mountain passes, and to use caution during periods of heavy rain or thunderstorms.
Another round of precipitation may follow Monday into Tuesday as forecasters track slower-moving components of the system.
More: Incoming atmospheric river storm will cause more flight problems. See forecast.
How much rain will California get this week?
Some areas can expect to see heavy rain and snow from this weather event. These are the estimated rainfall totals, through Nov. 19, according to the National Oceanic and Atmospheric Administration.
Southern California / Palm Springs area: ~1 inch in lower deserts, 2–5 inches in surrounding mountains. Risk of localized flash flooding in desert washes.
Los Angeles / Ventura / coastal Southern California: ~1 inch near the coast, with heavier totals inland and in the mountains; urban flooding possible.
Central Coast / San Francisco Bay Area: ~1–2 inches near coast, higher amounts in hills and upslope areas; isolated flash flooding possible.
Sierra Nevada: 3–5+ inches in mountains, with heavy snow at high elevations; risk of mountain travel impacts.
Northern California coastal ranges / southern Oregon: 2–4 inches, locally up to 6 inches in the heaviest bands.
Central Valley: 0.5–1.5 inches, with heavier totals near foothills; moderate flood risk along rivers and low-lying areas.
As for the timing of the rain, AccuWeather senior meteorologist Heather Zehr said, “the bulk of the rain for San Francisco and the Bay Area in general will fall from Wednesday night, Nov. 12, to Thursday morning, Nov. 13.”
“For the Los Angeles area, the rain should be the heaviest for the Thursday afternoon and evening rush hour on Nov. 13,” she said. “Most of the rain will fall on San Diego during Thursday night and may have departed by the Friday morning rush hour.”
What is an atmospheric river? How does it differ from a standard storm system?
On the West Coast, atmospheric rivers approach from the Pacific Ocean, carrying tremendous amounts of water. They occur most frequently during specific weather patterns, including El Niño, which can increase their frequency or intensity; however, they can also occur in other years.
These long, narrow corridors of air have been responsible for as much as 65% of the West’s extreme rain and snow events, USA TODAY formerly reported.
According to the National Oceanic and Atmospheric Administration, an atmospheric river — described as a “river in the sky” — transports water vapor outside of the tropics. While they vary in size and strength, the average system carries an amount of water vapor equivalent to the average flow of the Mississippi River at its mouth.
Past atmospheric rivers have caused widespread impacts. For example, earlier this year, two systems drenched Southern California, triggering severe flooding, tornadoes, avalanches, and mudslides. Cities including San Francisco and Redding received up to a month’s worth of rain, prompting evacuations and rescues from southern Santa Barbara to Orange County.
Is an atmospheric river the same as a ‘pineapple express’?
A “Pineapple Express” is a type of atmospheric river originating from near Hawaii, bringing warm, wet air and heavy rainfall to areas such as California and the Pacific Northwest.
According to the National Weather Service in Portland, the current atmospheric river is forming as a strong weather system over the Gulf of Alaska pulls in subtropical moisture and funnels it toward the region.
Meteorologists track these systems using a technique called integrated water vapor transport, which measures the amount of moisture moving through the atmosphere. High readings on this metric are a key indicator that an atmospheric river is approaching.
How to prepare for an atmospheric river
The weather service in Portland said residents should take these steps to prepare for the heavy rain:
Check your home’s gutters and clean them out if there are leaves from recent winds.
Practice caution around low water crossings, where street drains may back up and cause rain to pool.
Slow down while driving off interstate and bridge ramps and when making turns. Recent heat has caused oil in the road to come to the surface, making roads slick when rainfall is added.
Expect creeks to rise and have more flow in the Coastal Range, Willapa Hills and Cascades.
Check your local weather forecast for expected rainfall amounts and timing.
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Brandi D. Addison covers weather across the United States as the Weather Connect Reporter for the USA TODAY Network. She can be reached at baddison@gannett.com. Find her on Facebook here.
This article originally appeared on Palm Springs Desert Sun: Atmospheric river to bring rain, snow to California. See totals by city