By AccuWeather Meteorologist
Published Dec. 22, 2021 10:00 AM EST | Updated Dec. 24, 2021 5:19 AM EST
A potent storm that took aim at the Northwest earlier in the week dropped down into California on Wednesday, setting the region up to receive drought-relieving rain and snow -- and the rainfall could set records on Christmas Eve.
Increasing amounts of moisture moved onshore on Wednesday with snow developing across the Sierra Nevada mountain range. This will be the beginning of an extended stretch of wet weather for the Southwest, according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok.
On Wednesday night, much-needed rain continued falling across the California coast, including San Francisco and San Jose, California. Snow also began across the Sierra Nevada as well as parts of the Klamath Mountains. By midday Thursday, San Francisco had picked up nearly 2 inches of rainfall thus far. Fresno was nearing 0.50 of an inch of rain.
Heavy rain caused an underpass in Millbrae, California to flood Thursday morning. A vehicle was submerge as a result of the flooding. Two people were found dead inside the vehicle, according to CBS San Francisco. Sheriff's Detective Javier Acosta said the fire department noticed a person standing on the roof of a vehicle when they noticed a second vehicle was submerged.
"After they rescued the first person, they tried to gain access to the vehicle in the water. However, the conditions changed rapidly and it became too dangerous for the responders. The water was rising very rapidly and they had to retreat," said Acosta.
Heavy rain as depicted by the dark green, yellow and red colors on radar can be seen across California midday Thursday. (AccuWeather)
Rain continued in portions of Northern and Central California into Thursday evening, and it is also anticipated to stretch southward into Los Angeles and eventually San Diego. Heavy rain will pound these areas on Friday.
On Thursday afternoon, Nevada Governor Steve Sisolak announced an early closure of state government offices in Northern Nevada due to dangerous road conditions from continued flooding. "After investigation, it was determined the 'explosion' noise heard was likely the rock at the dam cracking. Water will begin to get released from the Twain Harte Lake which will create a rise in water levels down stream," Tuolumne County Sheriff said in a Facebook post.
Also on Thursday, an evacuation advisory was issued for some residents in Twain Harte after cracks were found in a dam. Water is being released from the lake which will contribute to rising water levels downstream. This comes as the area experiences heavy snow, rain and wind.
"Across Southern California, Thursday night and Friday will be downright miserable for those driving to family gatherings and church services or going to pick out that last-minute Christmas tree," said AccuWeather Meteorologist Reneé Duff. Heavy rain could even impact portions of Arizona on Friday and Friday night.
"Heavy rain is expected to spread over places such as Los Angeles and San Diego, which can lead to ponding of water on the roadways and significantly reduced visibility," warned Duff, adding that excessive water runoff can even lead to localized flooding and mudslides, especially in burn-scar areas.
North of San Bernardino, reports of stranded vehicles, washed-out guard rails and roadways came in late Thursday evening according to Caltrans. Roads such as SR-18 and SR-38 were a few of the roadways impacted.
Officials recommend motorists leave extra space between cars, stay aware of their surroundings and slow down. Driving with caution can help avoid countless accidents during the holiday season.
By Monday morning, up to 8 feet of snow is expected to fall across the highest elevations of the Sierra Nevada, with at least 3-6 inches of snow in places like Medford, Oregon, and Reno, Nevada. This could cause significant travel delays, particularly on slippery pass roads. Winter storm warnings have been issued for parts of Northern and Central California including around the Lake Tahoe area in California's Sierra Nevada.
However, snow isn't the only precipitation that could be measured in inches from this event.
"A general 1-2 inches of rainfall with locally higher amounts are forecast for the end of the week across Southern California, which could make for the wettest Christmas Eve on record in some cities," said Duff.
One of those cities would be Los Angeles, home to nearly 4 million people, which has only had three Christmas Eves where the downtown area has recorded more than 2 inches of rainfall since record-keeping began: 1892, 1916 and 1971.
"2021 could become the fourth depending on the exact timing and intensity of rainfall, and at least an inch of rain in the city seems like a sure bet," said Duff. Anywhere from 2-4 inches of rain could fall in the mountains around Los Angeles. This may even seem reminiscent of when the city received over 2 inches of rain earlier in the month on Dec. 14.
Sacramento, Redding and Fresno could also measure at least an inch from the storm this week, with San Francisco likely having 2-4 inches through Monday morning. Rain on Friday could be even heavier south of the City of Angels, particularly around San Diego.
"In San Diego, Dec. 24, 1940, holds first place for the most amount of precipitation on Christmas Eve with 1.47 inches of rainfall," Duff said.
Forecasters predict this amount has a good chance of being toppled on Friday. Even though San Diego reported just under an inch of rain with the last storm on Dec. 14, rainfall amounts remain around 66% of December's average as of Thursday.
Another city that could potentially smash daily precipitation records is Palm Springs, California.
"In Palm Springs, Christmas Eve in 1959 was the wettest on record with 0.44 of an inch of rain, but more than an inch is expected with the coming storm," added Duff. The city received even less rain than the other cities from the previous storm, with less than a third of an inch falling on Dec 14.
While all this rain might be a nuisance for one of the busiest travel times of the year, it could also help relieve some of the drought conditions weighing on the Southwest. Nearly 30% of California is experiencing exceptional drought conditions, according to the United States Drought Monitor. More than 80% of the state is in extreme drought.
Although Los Angeles is on track for its typical December rainfall, the city has received just half of its yearly average so far.
Rain and mountain snow likely won't stop early next week, and waves of moisture are expected to continue pounding the region through the end of December. Some of this snow could even be heavy enough to shut roads down.
"Multiple periods of heavy snow over Donner Pass can close I-80 for a time," said Pastelok, emphasizing the major travel issues that could ensue between Christmas and New Year's Eve.
For those weary of the seemingly endless parade of storms, AccuWeather long-range forecasters predict storms in the West will pack less of a punch after the calendar turns to 2022.
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