Sometimes in the weather business, things happen in a short period of time.
This is such a period.
We will experience:
1. Coldest temperature in several years on either side of the falls
2. A freezing cold shower, especially in Gorge, north of the Willamette Valley and south of downtown Seattle.
3. Strong easterly winds reaching hurricane strength in the Columbia Gorge and passes.
4. It warms up quickly this weekend, with typical rains and mild conditions again.
Phase 1. Arctic air
Eastern Washington has been very cold, with some temperatures dropping below zero last night. The temperature in Western Washington was much lower than usual.
To illustrate, here is the low temperature this morning. To the west of Washington, primordial cold air is pushing southwest through NW Washington’s Fraser River Valley.
Tonight, even colder air will move in, along with good radiation cooling into space due to thinning clouds overhead. Temperatures will drop as low as teens get out of the water in western Washington.
Stage 2: Strong East Wind
This large pressure difference will create extremely strong easterly winds (from the east) that pass through the Cascade Passes and especially the Columbia River Gorge. Winds from Cascade Locks to Troutdale in Gorge could reach more than 60 mph–and this would be arctic cold air from eastern Washington.
Strong easterly winds will also blow down the western slopes of the WA Cascades, with gusts from North Bend to Enumclaw, with winds accelerating westward down the Juan de Fuca Strait. (see wind gust map at 10 a.m. Thursday). Green and blue are the strongest winds.
Stage 3: Freezing rain
We will have cold air in place. And then a Pacific-front system with lots of moisture will approach late Thursday night through Friday morning. A forward system will move in warmer air overhead.
Here’s the precipitation forecast for 1 a.m. Friday–very humid.
Now, initially, precipitation will fall like snow across the region.
But that won’t last as the front is filled with warm air from the south.
And this sets up a freezing rain situation. Let me explain using the picture below.
Initially, (right side of figure) the atmosphere was cold enough for heavy snowfall (almost all precipitation in our region during winter starts when the snow is overhead)
But as the front drew near, the frozen air above pushed up and the snow began to melt into droplets.
Initially, the cold air is deep enough for the melted droplets to solidify into small ice balls: this is sleet.
But eventually, when the warm air above is deep enough, the water droplets at the top don’t have time to freeze but cool enough to become cold. super cold water...water is liquid but still below freezing.
Then, when this supercooled water hits a cold surface (and it gets cold), it freezes on contact creating… cold rain!
The latest Central Europe forecast for freezing precipitation is shown below.
By 3 a.m. Friday, freezing rain was heavy in the coastal mountains and was beginning to spread inland.
By 4 p.m. Friday, you could see a substantial total freeze in precipitation south of Puget Sound, Columbia Canyon and north of the Willamette Valley.
And by 4 a.m. Saturday, the ice was piling up in the Columbia Gorge.
On Saturday, it all turned to rain.
Either way, this looks like a major freezing rain event for the region. Airlines will have to get ready at SeaTac and Portland in particular, with Friday mornings particularly rough.
