More Flooding This Week, Colder in Mid February?

We finished January on a stormy note. I headed up to Whidbey Island last Friday night the 31st to visit my folks, and we lost power on my way up due to strong southerly winds from an atmospheric river that was aimed primarily at NW Washington and Vancouver Island. We are located at the very southern tip of Whidbey Island and are on the “tail end” of the power grid there, so we are often some of the first people to lose power on the island. It doesn’t help that the road leading south to our house is surrounded by tall, shallow-rooted, evergreens either!

This atmospheric river dropped up to 8 inches of precipitation over the Olympics and North/Central Cascades, and with snow levels near 8,000 feet, almost all of this precipitation was in the form of rain. There was a massive mudslide just south of Bellingham that blocked I-5 in both directions, and many rivers off the Cascades and Olympics saw moderate or even major flooding on Saturday. Benjamin Jurkovich of Washington Storm Chasers shot this amazing footage of the Stillaguamish at major flood stage at Granite Falls. There’s a fish ladder there but I doubt any salmon were climbing it on Saturday!

NEW #VIDEO! The granite falls waterfall/fish ladder is absolutely raging this morning on the Stillaguamish River. It is 6 1/2 feet higher than it was the other day we filmed at this location. Multiple homes down stream are also flooded unfortunately. #wawx #flood @NWSSeattle pic.twitter.com/HEMryJGS86

— Washington Weather Chasers (@WaWxChasers) February 1, 2020

As a whole, January was warm and wet. Taking a brief look at stats posted on social media, Seattle and Portland saw rain 28 our of 31 days, tying records set in 2006 and 1956, respectively. It rained in Forks, WA every day of the month for a new all-time record of 30.78,” and Portland saw its warmest January since 1953.

February started off dry and chilly, and there were even some reports of a dusting of snow above 700 feet Monday morning across the southern Portland metro area. However, things are about to turn a whole lot wetter as yet another atmospheric river stalls over the area, renewing river flooding concerns.

While the atmospheric river that affected us last week had a more typical, SW-to-NE orientation, this atmospheric river is gliding over the top of a strong ridge of high pressure in the Eastern Pacific and is moving into our region from the WNW. Note that the atmospheric river still has subtropical origins; it just is directed southeastward as it is steered by the clockwise flow around this strong Eastern Pacific high.

Westerly Atmospheric Rivers (WARs) are a subtype of atmospheric river that, as the name suggests, arrive from the west. The westerly component is notable because the major population centers in the Puget Sound lowlands and Willamette Valley are typically rainshadowed during these Westerly Atmospheric Rivers, while the Cascades, which are perpendicular to these WARs, get hit extraordinarily hard and can see widespread major flooding. A textbook example was the WAR of January 6-7 2009; Friday Harbor, which sees rainshadowing under southwesterly atmospheric rivers, saw 1.61 inches, while normally-rainier Everett only saw 1.04 inches. Rain totals in the Cascades were prodigious, and the Snoqualmie River crested to an all-time high at Carnation. The below video was taken at Snoqualmie Falls on January 8; the closest I’ve ever seen the river to being that high was on November 7, 2006 when Carnation also set a (then) record crest.

Because our current atmospheric river has a slight northerly component, places like Olympia that are normally far outside of the Olympic rain shadow are seeing significant shadowing while Sequim and the San Juan Islands are seeing moderate/heavy precipitation.

The Cascades are getting clobbered, and as of Tuesday night, precipitation is in the form of snow all the way south to Tinkham Road along I-90. Snoqualmie Pass is open, but chains are required in both directions. Check out my I-

Forecast:

This atmospheric river will stall over Washington and NW Oregon through Friday, bringing extremely heavy rain to the west slopes of the Cascades/Olympics, almost no rain for Eastern Puget Sound and the Willamette Valley, and moderate rain in locations outside the rainshadow. The graphic below shows the 72-hour total ending 4pm Friday – note the whites (10+ inches) over parts of the Central Cascades and even the Blue Mountains in NE Oregon. The strong, moist, stable flow with these atmospheric rivers is extraordinarily effective at enhancing precipitation on windward slopes.

Snow levels will rise from around 1,500 feet tonight to 5,000 – 7,000 feet tomorrow afternoon and stay there through Thursday night. Freezing levels will fall slightly on Friday as an upper-level low moves through and should be back to pass level on Saturday just in time for ski bums to hit the slopes. Beware; under that enticing layer of power on Saturday will lie a frozen, rain-soaked mess.

The same rivers that saw significant flooding last week will see similar flooding this week, with the Snoqualmie and Tolt expected to reach major flood stage (purple). No rest for the weary there!

After cooler weather and showers Friday and Saturday with this upper-level trough, we’ll see partly cloudy skies Sunday and Monday with near-average temperatures. Chilly, wet NW flow returns Tuesday and Wednesday, and by Thursday 2/13, we could be talking about the potential for a more significant arctic outbreak. The Climate Prediction Center certainly thinks so!

I’ll leave you with one image from the GOES-17 satellite of this atmospheric river stretching all the way west of Hawaii into the Pacific Northwest. Have a great night, and I’ll keep you posted on our active weather this week and the potential for colder weather towards the middle of the month.