New storm with rain, snow already eyeing Northwest
A new storm will roll ashore in the northwestern United States before the middle of the week and could bring enough rain to lead to flooding problems, AccuWeather meteorologists warn.
The first storm that moved in over the weekend finished up early Tuesday morning with mixed snow and rain at many of the passes and heavy snow over the high country. This storm was the most widespread, significant precipitation producer of the season so far and will soon be followed by a second storm of similar magnitude with up to several feet of snow likely to cover the high country slopes by Thursday night.
"Snow levels will rise ahead of and during the first part of the new storm," AccuWeather Senior Meteorologist Adam Douty said. That means rain will fall during much of the first half of the new storm over the passes. However, there can be drenching rain, fog and even some rockslides that can knock debris onto the roads in the steep terrain or where the roads cut through the mountainsides.
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At the lower elevations, especially along the lower west-facing slopes of the Cascades, Coast Ranges, and the Olympics, 4-8 inches of rain will fall from through Thursday night, with local amounts near a foot. Enough rain can pour down along the streams and rivers flowing out of the mountains in this setup to lead to flooding.
Cumulative rainfall totals this week from both storms will likely range from 1.50 to 2 inches in Seattle and 1 to 1.50 inches in Portland, Oregon. While the rain will not lead to serious flooding in the metro areas, some water can quickly run off and lead to urban-style flooding and travel delays along much of the Interstate 5 corridor. Rain and gusty winds can also lead to airline delays at Seattle-Tacoma International Airport and other regional travel hubs.
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During the second part of the storm, from later Wednesday to Thursday, colder air will sweep in, and snow levels will dip over the Cascades. Some slush can build up over the passes from late Wednesday night to Thursday night.
Farther south, a second storm will bring more rain and high-country snow to the Siskiyou and northern Sierra Nevada in California. Most of the accumulating snow will fall above the crest of Donner Pass, California, along I-80. Still, there can be a period from Thursday night to Friday when the air will get cold enough for accumulating snow to fall over the pass with slow and slippery travel.
Along with the varying snow levels, periods of gusty winds typical of winter will occur over the mountains and through the passes, leading to some travel issues for motorists.
The late-week storm may also bring some of the first showers of the season to parts of Southern California, including the Los Angeles area. The most likely places to get enough rain to run off a bit will be in the west-facing slopes of the mountains and hillsides.
AccuWeather meteorologists are monitoring another potential Santa Ana wind event for Southern California this weekend. The setup will depend on the orientation of an area of high pressure to the north and the strength and position of winds at the level where jets fly over Southern California.
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Winds might not be as strong as those from late last week when several large fires broke out. Still, the situation may change, and stiff breezes from Sundowners or weak to moderate Santa Anas can create dangerous fire weather conditions.
Another storm is forecast to drop into the Northwest over the weekend bringing colder air that can translate to lower snow levels and possibly snow accumulation over the Cascade passes in Washington and Oregon.
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