San Francisco, Los Angeles to receive more heavy rain
After a storm moves through the state on Monday, a larger and more disruptive storm is forecast to hit the region later this week.
More moisture-packed storms are expected to pay a visit to California during the first week of 2023 following an atmospheric river that dropped a historic amount of rain on the San Francisco Bay area as well as heavy snow in higher elevations on New Year's Eve.
Because of the saturated state of the ground, another atmospheric river during the middle and latter part of the week will lead to more flooding and mudslides in the Golden State, AccuWeather meteorologists warn.
Meteorologists describe an atmospheric river as a plume of rich moisture that extends from the tropical part of the ocean to land and can produce copious amounts of rain and mountain snow should the firehose effect linger.
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More rain is coming to much of California this week, forecasters say.
A weaker storm, when compared to the one that moved through on Saturday, affected much of California on Monday and Monday night. Rainfall with this storm has been relatively light, generally ranging from a few tenths of an inch to about 1 inch.
Spotty leftover rain showers and mountain snow showers will linger on Tuesday.
However, the storm system that started the week will be followed by a larger and more disruptive storm in a matter of hours.
A much more potent storm will be waiting in the wings over the Pacific and that system is poised to overspread Northern California on Wednesday. While this storm may have a less-intense firehose effect from the ocean, compared to Saturday's storm, it will still unload heavy rain and result in flooding and mudslides.
"The storm is likely to gain strength and slow down as it approaches California at midweek," AccuWeather Meteorologist Joe Bauer said. A narrow ribbon of tropical moisture will extend from near Hawaii to parts of California for a time.
As the storm stalls, it will pump large amounts of moisture over much of California for an extended period from Wednesday night to Thursday night.
"The slow-moving nature of the storm and its moisture will lead to multiple hours of moderate to heavy rain at low and intermediate elevations of California," AccuWeather Senior Meteorologist Joe Lundberg said.
A general 2-4 inches of rain will fall from the storm in San Francisco, as well as coastal areas and the west-facing mountains farther to the north and farther south through Big Sur and perhaps to Santa Barbara, California, according to AccuWeather's team of meteorologists. Some coastal areas from north of Los Angeles to just south and north of San Francisco are likely to receive between 4 and 8 inches of rain from the storm.
The Los Angeles area could receive a general 2 inches of rainfall from the storm with lesser amounts forecast toward San Diego. Should the atmospheric river set up farther south than the Big Sur area, then more of coastal Southern California could receive heavier rain, which would lead to a greater risk of flash flooding and mudslides.
The mid- to late-week storm will result in a high risk of dangerous and perhaps life-threatening flash flooding and mudslides, especially in the northern and central parts of California. Motorists may need to seek alternative routes as water flows across and collects on low-lying portions of streets and highways. Winding, hilly secondary roads may be especially dangerous in this situation where debris is deposited or the pavement is washed away.
The saturated state of the ground combined with gusty winds from the major storm from Wednesday to Thursday can lead to trees toppling over. When trees come down, power outages often result.
Unlike the storm during the New Year's weekend, which began as rain before transitioning to heavy snow, the storms this week will have cooler air to work with.
The quick change from rain to intense snow on Saturday caused Interstate 80 to become clogged with stalled vehicles as inches of snow evolved into feet of snow.
Snow levels this week will close to Donner Pass and Truckee, California, for the majority of the periodic wintry conditions. However, since the main focus of the storm's moisture will be directed toward coastal areas of California, rather than from the coast to the Sierra Nevada, snowfall is likely to average 6-12 inches with locally higher amounts over the mountains, instead of the several feet of snow that quickly piled up on Saturday.
This image depicts what the plume of moisture may look like on Wednesday, Jan. 4, 2023. (AccuWeather Future Radar)
As more snow piles up in the high country of the Sierra Nevada, the risk of avalanches will increase.
The Pacific storm train is likely to continue through next week, but conditions will continue to evolve during the middle portion of January.
Changes in the jet stream and surface weather patterns will put some resistance on the amount of moisture available to the storms in California, moving forward during the middle of the month, Bauer said.
"There will be storms with some episodes of rain and mountain snow in California during the second and third weeks of January, but the strongest storms and heaviest precipitation are likely to be focused more on the northwest U.S., rather than farther to the south," Bauer said.
The Pacific storm train is likely to continue through next week, but conditions will continue to evolve during the middle portion of January.
Changes in the jet stream and surface weather patterns will put some resistance on the amount of moisture available to the storms in California, moving forward during the middle of the month, Bauer said.
"There will be storms with some episodes of rain and mountain snow in California during the second and third weeks of January, but the strongest storms and heaviest precipitation are likely to be focused more on the northwest U.S., rather than farther to the south," Bauer said.
This image shows current reservoir levels as a percentage of the average for Jan. 1, 2023.
In terms of drought relief, the storm train has already been beneficial. Many reservoir levels in California were on the rise during late December. Runoff from prior and upcoming storms will continue to raise water levels in the many rivers and reservoirs in the coming days.
As runoff continues over the next several weeks, it is possible for some reservoirs to approach full capacity in the northern and central parts of the state.
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