Residents throughout California were dealing with the threats of scattered flooding, mudslides, heavy snow and hazardous travel on Tuesday as another powerful storm lashed the West Coast.
Here are the key things to know:
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Tuesday’s storm is the second in a series of three atmospheric rivers expected to strike the state over a week.
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Northern California was already saturated by heavy rain last weekend. With more rain incoming, flood watches were in effect for roughly 13 million people through Wednesday morning, including in heavily populated areas like the San Francisco Bay Area and Sacramento Valley.
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As that storm drifts south, Southern California could see an inch to a few inches of rain from Tuesday through Friday. Dry conditions there helped fuel disastrous wildfires in and around Los Angeles last month, but too much rain, too fast, could lead to mudslides in areas that were burned. This week, the hourly rain rate should lead to only minimal mudslide risk.
Northern California gets another round of rain, and maybe a thunderstorm.
Forecasters warned that the rain last weekend in Northern California had saturated the ground, priming some northern regions for flooding as new rain pours down this week. By the end of the week, the Sacramento Valley and areas south of San Francisco may see another one to three inches of rain. North of the city, forecasters predicted an additional two to four inches.
Between Monday and Tuesday, the atmospheric river shifted into the Bay Area and northeast through Sacramento, bringing more intense rainfall and heavy snow from the Golden Gate to the Sierras. The forecast continues to show this stream of moisture meandering like an uncontrolled fire hose right along Interstate 80, which runs from San Francisco through Sacramento and over Donner Pass toward Lake Tahoe.
Since last Friday, some reporting stations, like Brush Creek Ranger Station in the mountains just northeast of Lake Orville, have measured over a foot of rainfall, with more on the way. An additional three to six inches of rain is possible across the Sierra Nevada foothills, and another two to four inches of rain is possible over the coastal ranges.
The heaviest rain on Tuesday may come later in the day, possibly even as rare thunderstorms during the afternoon bring lightning, stronger winds and heavier rain through the Bay Area. A water spout or two may form as the stronger storms push ashore.
Once the strongest storms move through, there will be a brief reprieve on Wednesday. But it won’t last long. The third atmospheric river in this series approaches Wednesday night into Thursday.
That next system “looks a good deal weaker than the current atmospheric river, with less rain and lighter winds,” forecasters with the National Weather Service in San Francisco said. Most areas will receive a more manageable amount of rain, probably less than an inch, before things dry out on Friday.
Even though the third system might be weaker, the Sierras may still squeeze out another foot to three feet of snow by the end of the week.
Rain will arrive in dry Southern California.
Atmospheric rivers are a typical part of winters in California, but so far this season, they have not brought their soaking rains to the southern part of the state. That’s changing this week.
And while the rainfall in the southern parts of the state isn’t expected to be as intense as in the north, even a moderate amount of rain could be disastrous for areas of Los Angeles, where the landscape was ravaged by wildfires last month. But forecasters believe this rain is likely to be more of a beneficial steady rain instead of a raging downpour, which should limit the amount of debris flowing over the burn scars in the region.
The storm will most likely peak in Southern California from Tuesday night into Wednesday, with an inch of rainfall, or even higher in the mountains and valleys of San Luis Obispo and Santa Barbara Counties. Los Angeles and Ventura Counties may see far less. However, up to two inches of rain may fall on south-facing slopes, including those on the Santa Barbara South Coast, Malibu and the foothills of the San Gabriel Mountains.
After a brief lull Thursday morning, the third, potentially weaker system will arrive, bringing widespread rainfall across the region. The storm’s rainfall is expected to taper off Friday afternoon, and the rain threat should end by the evening.
Southern California has been critically dry this winter, and the lack of rain helped fuel last month’s destructive wildfires. And while these two systems might not produce enough rainfall to quell high fire season altogether, forecasters said, “it will, for sure, greatly lessen the danger over the next week or two.”
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