Multiple Atmospheric Rivers to Bring Heavy Rain and Snow to Northwestern US
CNN – Multiple atmospheric rivers are expected to roll across the northwestern US over the next few days, bringing heavy rain, feet of snow, and strong winds. In total, more than half a dozen western states are under some type of winter weather alert Sunday as these atmospheric rivers spread from Washington and Oregon eastward into Colorado and Wyoming.
An atmospheric river (AR) is a plume of moisture that helps carry saturated air from the tropics to higher latitudes, delivering unrelenting rain or snow. This sequence of back-to-back atmospheric rivers, called an AR family, began Saturday and will continue across the region through Wednesday without much of a break period in between systems, leading to an increased risk for flooding.
“The Winter Storm Severity Index (WSSI) shows major impacts are possible in the highest elevations of the Pacific Northwest and the Rockies, likely causing hazardous to even impossible travel conditions in these impacted areas,” the Weather Prediction Center cautioned.
At least 5 to 10 inches of rainfall is forecast along the coastal areas of Oregon, Washington, and northwestern California. For higher elevations, as much as 1 to 3 feet of snow is expected to accumulate through the weekend. An avalanche warning has been issued for areas of Oregon and Washington as well.
The Northwest Avalanche Center in Seattle said, “Very dangerous avalanche conditions will develop over the next 24 hours. Travel in avalanche terrain in not recommended.”
Gusty winds up to 50 mph are also likely and could bring down trees and power lines. A level 4 out of 5 AR event is forecast to hit the entire coastline of Oregon. Not all atmospheric rivers are bad, with event levels 1 and 2 considered mostly beneficial rains, but levels 4 and 5 are considered more hazardous, with the risk for flooding and travel dangers outweighing the benefits.
The Weather Prediction Center said, “Given enhanced rainfall during the weekend, the soils will be more vulnerable and thus the potential for greater run-off and flooding. Snow levels are initially expected to be rather high, and therefore western facing slopes of the Cascades may be subject to an additional risk of flooding due to snow melt.”
A slight risk for flooding, a level 2 out of 4, has been issued for Sunday, Monday, and Tuesday across western Oregon and Washington in anticipation of excessive rainfall amounts.
Meteorologists and weather experts are advising residents in the area to take necessary precautions and stay up to date on weather alerts as these atmospheric rivers continue to impact the region.