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| Snoqualmie Falls in Washington State is at its highest level in at least a decade due to this week's atmospheric river. Major flooding is occurring or forecast on at least 18 river sites in western Washington. Photo via Facebook, Washington Weather Chasers |
Round One of the flooding hit yesterday and last night, with major flooding and some reports of record high crests on some rivers.
Seattle area meteorologist Scott Sistek, in his Emerald City Weather Blog, painted a pretty grim picture of the flooding underway in 'Washington State:
"The Skagit River is now forecast to reach several feet beyond its record crest. The predicted peak at out Vernon was 41.54 feet Thursday night - over 4 feet above the record crests from 1990, 1995 and 2021.
The Snohomish River at Snohomish forecast was back at peaking a few inches over record flood stage Thursday and Friday."
Sistek went on to describe several other rivers that have or are expected to reach record crests.
The flood in Washington is coming in two waves. The atmospheric river moved south into Oregon yesterday, so the rain largely stopped in Washington and rivers started to recede.
But now that atmospheric river off the Pacific Ocean is back in Washington. This time around, the rainfall isn't quite as heavy as in the first round, but will last longer than in the initial blast. With rivers already flooding or at least very high, it won't take much for the major flooding to take hold again today.
To make matters worse, forecasts for amount of rain in today's wave of the atmospheric river in Washington have increased.
Eighteen river locations in Washington are expected to reach major flood stage. Washington Gov. Bob Ferguson said the state's Emergency Operations Center is at level 1, the highest response level.
The weirdest part of this is in northern Idaho. Atmospheric rivers with heavy rain hit the Pacific Northwest most winters. The moisture sometimes carries over all the way to the mountains of Idaho, producing some rain in the valleys and nice winter storms with heavy snow in the Bitterroot Range ad other tall Idaho mountains.
This time, the atmospheric river is much stronger than usual. The moisture, and the tropical air associated with it, is raising flood concerns in the normally wintry mountainous terrain of Idaho.
Total rainfall in much of central and northern Idaho was expected to be in the higher elevations and one to four inches in the valleys. Snow levels were expected to rise to maybe 6,000 feet to as high as 9,000 feet, which is pretty wildly high for December.
Record high temperatures are also melting existing snow. As you can imagine, this is a recipe for high water.
The atmospheric river is strong enough so the some moisture will probably make it over the Continental Divide into Montana. There, the wet air will collide with a blast to Arctic air coming in from Canada to produce heavy snow and strong winds across much of Montana late this week.
An atmospheric river is a long narrow band of moisture that can travel thousands of miles before making landfall. They can happen almost anywhere near a coastline, but they are common in the winter along the Pacific coastlines of the United States and Canada.
Many of them are beneficial, as they bring needed rain and mountain snows to the West Coast. However, stronger ones, as we're seeing now, can cause serious flooding.
Climate change can make atmospheric rivers warmer and wetter than they otherwise might be. That increases the risk of flooding. The added warmth also makes rain more likely and snow less likely up in the mountains.
That less mountain snow scenario can increase flooding, since rain fall where it normally snows. High elevation rain also reduces the winter snow pack. That leaves less snow to melt in the spring to feed into reservoirs.
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