Travel delays to mount in California and Southwest as storm moves in with downpours, mountain snow
A brief, but high-impact storm will bring heavy rain, feet of high country Sierra Nevada snow and hazardous travel to California and neighboring states from Wednesday night to Thursday night.
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A potent storm is expected to move in from the Pacific Wednesday night and Thursday, bringing drenching rain, heavy mountain snow and travel disruptions to the West Coast of the United States, especially in California, AccuWeather meteorologists warn. The storm is poised to bring heavy rain to the deserts as well for the weekend.
Warmth will linger along the Pacific coast states until the storm's arrival.
Soon after rain begins Wednesday night, temperatures are expected to drop sharply over the Sierra Nevada, allowing snow to accumulate quickly above the passes in northern areas. Over the ridges and peaks above 8,000 feet, a couple of feet of snow and blizzard conditions are possible as strong winds develop.
At Donner Pass, California, along Interstate 80, most of the storm will bring rain or a mixture of rain and wet snow from late Wednesday night through much of Thursday.
During the latter part of the storm, temperatures are forecast to drop, resulting in a period of heavy snow Thursday night. Whiteout conditions and several inches up to a foot of snow are possible, depending on the speed of the changeover. Regardless, treacherous travel is anticipated over the summit.
"Travelers should monitor the latest conditions and be prepared for snow-covered roads and possible closures," said AccuWeather Senior Meteorologist Heather Zehr.
"For the Lake Tahoe, California, area, which is a bit lower in elevation, rain during Thursday and midday will be followed by a change to wet snow Thursday night before ending," AccuWeather Senior Meteorologist Brett Anderson said. "From 1 to 3 inches of slushy snow seems likely at the resort area." Temperatures are not expected to fall quickly enough for snow over the Southern California passes, but rain, wind and fog could still lead to hazardous travel conditions in the mountains.
Over much of California's lower elevations, the storm will bring a period or two of drenching rain that could lead to ponding, flash flooding and mudslides.
Winds will howl along the coast and over the ridges and through the passes. Significant travel delays are likely due to rain during the height of the storm, affecting both roadways and airports.
"The bulk of the rain for San Francisco and the Bay Area in general will fall from Wednesday night to Thursday morning," Zehr said. "For the Los Angeles area, the rain should be the heaviest for the Thursday evening rush hour. Most of the rain will fall on San Diego during Thursday night and may have departed by the Friday morning rush hour."
Approximately 1 inch of rain is likely around Los Angeles. Lower rainfall totals are expected in San Diego and higher amounts to the north along the California coast and along the west and southwest-facing slopes of the Coast Ranges and in the lower elevations of the Sierra Nevada, Siskiyous and Oregon Cascades.
A general inch or so of rain is likely in San Francisco. From 2 to 4 inches of rain is likely along the lower, seaward-facing slopes of the coast ranges in Northern California and southern Oregon. The AccuWeather Local StormMax™ rainfall for the storm is 6 inches.
There may be a slight split in the storm's rain and mountain snow in parts of Oregon, with another wave of precipitation likely in Washington and southern British Columbia from late Wednesday to Thursday. Rain is expected over the Cascade passes in Washington due to the storm.
Colder air, lingering moisture and the arrival of a second, weaker storm could produce snow over the passes Friday, creating slippery travel conditions across the Northwest.
Weekend desert downpours loom
As the main body of the storm pivots inland, moisture from the tropical Pacific is likely to be funneled into the Southwest to end the week.
This setup will lead to an abundance of rain over the deserts from Southern California through Arizona and part of western New Mexico from Friday night to Saturday night.
So much rain may pour down, leading to flash flooding, as well as significant drought relief. Motorists should be prepared for urban flooding in Las Vegas, as well as Phoenix, Flagstaff and Tucson, Arizona, and Las Cruces, New Mexico.
Motorists should be prepared for rainy travel, poor visibility and ponding on stretches of interstates 5, 10, 15 and 40 in the region.
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