Over the last several weeks, atmospheric rivers have produced heavy rain, flooding, and mudslides. The most recent storm, possibly the most violent yet, slammed the region with heavy rain and devastating winds on Monday. Seems like these parts of the Pacific Northwest and British Columbia can’t seem to get a break.
What Is an Atmospheric River?
A narrow corridor or filament of concentrated moisture in the atmosphere is known as an atmospheric river.
Atmospheric rivers are narrow bands of accelerated water vapor transport that emerge along the margins of broad areas of divergent surface airflow, particularly frontal zones associated with extratropical storms that form over the oceans.
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What’s Happening Now?
On Monday afternoon, moderate to heavy rain fell across parts of northwest Oregon, western Washington, and southwest British Columbia.
Unlike other atmospheric rivers, which produce milder, steadier rain over a longer period, this one was dropping rain at rates of up to a half-inch per hour. 4.23 inches of rain fell in Custer, Wash., just a few miles from the Canadian border, on Sunday.
Between midnight and 7 a.m. local time, an additional 1.66 inches had fallen. Winds gusted beyond 50 mph as the rain fell. A slender but intense jet of moisture is being slung east by an atmospheric squeeze play, with low pressure banked to the north and a high pressure banked to the south.
Flooding and mudslides stopped part of Interstate 5 near Bellingham, Washington, on Monday, trapping three cars in the rubble. Nobody was seriously hurt. Due to hazardous travel conditions, all schools in the Bellingham and surrounding districts were closed on Monday.
Flooding was predicted in Sedro-Woolley, Burlington, and Mount Vernon as the water poured down the river.
What Is About to Come?
According to the National Oceanic and Atmospheric Administration, an atmospheric river walloped the area late last week with practically nonstop rain, and its tail end is coming with one final big push.
The atmospheric river’s effects will fade by Monday evening in Washington state, but its final act might be a rush of winds there and along Oregon’s coast, allowing the system to go out with a bang. There are high-wind advisories in effect until Monday evening.
According to weather predictions, Monday’s atmospheric river could be rated a Level 5 out of 5. Because atmospheric rivers convey the majority of its moisture at mid-levels of the atmosphere thousands of feet above the earth, the highest precipitation totals are realized at higher elevations.
Moisture is deposited on the windward side of the mountains by an air-driven up to them. The atmospheric river will leave Vancouver afternoon and Seattle by 3 or 4 p.m. local time on Monday. Coastal Oregon will only feel the effects for a few hours when the decaying band of juicy air swings southward and thins late Monday.
It will be lapping at the Bay Area in California by early Tuesday morning, with some light showers, while places to the south should experience nothing. Meanwhile, another storm system is expected to bring more rain to the Pacific Northwest late Thursday and early Friday.
The low-pressure system that is causing the atmospheric river deluges will sweep through southern British Columbia and Alberta on Monday night, intensifying its route to Saskatchewan. The ensuing pressure gradient, or difference in air pressure with distance, will stimulate winds speeding out of the west over the northern Plains and Montana, where high elevation wind gusts could surpass 100 mph.
The condition should improve by Tuesday after a series of rainfalls for six days, as predicted by the forecasters.