After multiple weeks without significant rain on the West Coast, an atmospheric river is poised to disrupt the spell of dry weather with heavy rain and mountain snow in Washington and Oregon before moving south, where it is expected to deliver multiple waves of heavy precipitation to Northern California into next week.
Coastal areas of Oregon and Washington could receive three to five inches from late Thursday into Saturday, while the coastal mountain ranges of Northern California are expected to be drenched during prolonged storm activity, with up to 15 inches of rain over the next week, according to the National Weather Service. The northern Sierra Nevada could pick up a foot and a half of snow.
The system will push into the Pacific Northwest on Thursday night before drifting south on Friday along the coast into Northern California, where it will linger through the weekend. Its band of moisture is expected to bring extended periods of moderate to heavy rain from into Northern and Central California Saturday into Sunday, and that region will see additional heavy rain on Monday and into the rest of next week.
Atmospheric rivers are ribbons of moisture carried by powerful winds. These storms have the potential to unleash deluges of rain, especially when they push up and over mountains. But their paths are narrow, and it can be difficult to pinpoint exactly where they will line up and release the heaviest rainfall. This early in the forecast, meteorologists can confirm a wet weather pattern is coming to the West Coast, but they’re less certain of the details, especially those next week.
This storm “is forecast to stall over California, wobbling up and down along the coastline,” said Roger Gass, a meteorologist with the Weather Service office in Monterey, Calif.
There’s a slight chance for excessive rainfall that could lead to flooding from Mendocino County south into the San Francisco Bay Area and as far south as Santa Cruz County from Saturday morning to Sunday morning, according to the Weather Prediction Center. The risk also stretches inland across the Sacramento Valley and into the Sierra Nevada. Streams are predicted to swell in southwestern Oregon and Northern and Central California, and the greatest potential for flooding is expected in Northern California.
“One of the more impressive things about this storm is how long it’s going to last in Northern California,” said Chad Hecht, a meteorologist at the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.
Here’s how things may unfold
-
Late Thursday: The system begins affecting the Pacific Northwest, delivering some rain and snow. In Seattle, rain is likely to start around Thursday evening.
-
Friday: The system spreads south into Northern California, while rain and snow continue to fall over Washington and Oregon. The system starts pushing into the Sierra Nevada late Friday.
-
Saturday: The system exits Washington early in the day and Oregon by later in the afternoon or evening, but it continues to soak Northern California, bringing snow over the Sierra Nevada.
-
Sunday: A chance for rain and snow continues mainly in Northern and Central California.
-
Monday through Wednesday: The system will tap into another big wave of moisture, likely on Monday, delivering continued rain to Northern and Central California into next week. (While some forecasters may refer to this round of precipitation as a second atmospheric river, Mr. Hecht described it as all part of the same massive system with multiple moisture feeds.)
While Washington, Oregon and Northern California saw wet starts to the rainy season late last year, they have not received significant rainfall for about two weeks. The dry period is starting to affect seasonal totals. Seattle has recorded about an inch of rain since Jan. 1, compared with five inches for a typical January.
With this storm, Seattle is expected to pick up an inch to an inch and a half of rain. “It’s not a big rain event, but it’s a change since we haven’t had much rain in two weeks,” said Kayla Mazurkiewicz, a forecaster with the Weather Service in Seattle.
San Francisco has not received any rain in more than three weeks and has seen little rain in all of January, recording less than a quarter of an inch since the start of the month. In a typical January, the city gets about 4.5 inches. The dry spell is coming to an end though, with San Francisco predicted to record over four to six inches over the next seven days. Just to the north, the mountains of the North Bay could receive more than eight inches.
Southern California has had one of its driest starts to winter ever, according to records going back more than 150 years. The dry conditions helped fuel multiple devastating wildfires across Los Angeles County this month.
While this system is expected to be focused over Northern California, it could bring up to an inch of rain to Southern California and Los Angeles County next week.
“Some forecasts have the rain tapering off before the storm gets down there, and others show it lingering and bringing some rain, but not a ton of precipitation,” Mr. Hecht said. “That’s not to say things can’t change.”
The post Powerful Storm System Set to Drench Northern California appeared first on New York Times.
