Weather Blog

Behold the backwards wind chill effect

Behold the backwards wind chill effect
OK, so I'm supposed to be off on paternity leave until February, but I'm on the late feeding shift tonight, and Scarlett's here in my arms by my laptop snoozing until her next feeding in 90 minutes or so, and there's interesting weather going on this Christmas Evening, so I figured, what better way to pass the time than a blog entry?

A Christmas weather riddle for you:

At 10 p.m. Christmas night, it was 43 degrees in North Bend, but a very chilly 25 degrees in Olympia.

If you were silly enough to step outside in short sleeves, which place would feel colder? The answer was -- they might feel just about the same.

OK, it was a trick question. In North Bend, the wind was gusting to 40-50 mph, making the wind chill around 25.

But! The point of this article was there were other places where it was windy, but not quite as windy, where it became more of a reverse wind chill effect in progress: It was warmer where it was windy than where it was calm.

We've all been outside on a cold, winter day where it's 35 degrees outside, then a gust of wind blows and it feels even colder -- perhaps 20-25 if the breeze is strong.

But Christmas night, the opposite effect was happening. Temperatures were a good 15-20 degrees different spread over not too far a distance. Other spots like Tacoma, Bellingham and Arlington were also in the 20s. Seattle? Upper 30s.

In our example tonight, the reason North Bend was 18 degrees warmer than Olympia was that east wind blowing through the Cascade foothills.

For the spots in the foggy 20s, a staunch inversion was in place where cold, dense air was pooled near the surface. And with little wind to mix up that cold air, it can just remain trapped there, and thus the air stagnation issues we've been having.

On the other hand, a strong arctic high pressure system centered in Eastern Washington is pushing a strong east wind through the Cascade passes and blowing pretty good into eastern King and Pierce Counties, as well as along the coast and western tip of the Strait of Juan de Fuca.

That wind is mixing up the cold air and bringing in some of the warmer air aloft, raising the temperature. (As a secondary warming bonus, that east wind also warms up as it sinks down the eastern slopes of the Cascades.)

So that's how you get some areas around here in the 20s with calm winds and fog, and others in the 40s with gusty winds but crystal clear skies -- a sort of reverse wind chill effect, except for the extremely windy areas, where to someone standing outside, the wind chill was low enough to overcome the warming effect the winds had in the first place.

(And if you were standing out there in short sleeves tonight, next year, ask Santa for a sweater :) )