Noon Thursday Update: Coldest day in years in Portland, precipitation arrives later

Everything is proceeding according to plan as they say.

Today is a rare sub-25 degree day in Portland. In fact we haven’t seen a day in the 20s since January 2017. Couple that with east wind gusts 35-50 mph and it’s bitterly cold out there (by Portland standards). If I read the numbers correctly, we’ve only seen 4 days with a high temp at/below 25 in the last 20 years! It’s cold...

Along with that, the wind is a big story. Peak gust is 46 mph at PDX so far, with some of the bridges seeing gusts to 50 mph. Rough driving, and a few trees are down here and there. The pressure gradient, the difference in pressure from The Dalles to Portland, is at 15 millibars! The highest I’ve ever heard of was an 18 millibar gradient during the east wind storm December 24th, 1983. I don’t think I’ve seen 15 millibars in my career, but maybe I’ve forgotten one. Regardless, very strong high pressure is squished up against the east side of the Cascades and wind is likely gusting well over 100 mph right now on those Vista House steps...at 15 degrees.

Precipitation is slow to arrive, as we’ve expected. Expect spots of flurries or ice pellets to appear in the next few hours, but my feeling is that anything significant that would freeze on roads and ice things up (liquid rain) will wait until after 5pm. That’s at the earliest. Models are indicating the transition to liquid rain could even wait until 7pm or so. That’s because it takes time for the warmer air to work in overhead. It needs to go well above freezing up around 3,000-5,000′ to change those snowflakes into raindrops. There will be a period this evening when we get ice pellets. That’s when this surface cold layer is so deep that the raindrops refreeze on the way down. They make that little “clinking” sound when they hit the ground, your car, or your head.

Then from 7-8pm or so onward, it’s ALL liquid rain through the rest of this event. Our forecast thinking hasn’t changed...up to 1/3″ ice glazing everywhere in the western valleys overnight through tomorrow afternoon, and a few spots may hit 1/2″ by Saturday sunrise.

ALL VALLEY LOCATIONS FROM LONGVIEW TO SALEM SHOULD STAY FROZEN UNTIL SUNRISE SATURDAY

Models are still in quite a bit of disagreement over when we switch to the warm south wind. So we’re sticking with the reliable “we’ve seen this before” forecast. That means cold air very stubborn to give way to those 55 degree southerly breezes! But that dramatic warming should finally happen Saturday for everyone except inner central and east Portland, and of course the Gorge.

The heaviest rain of this evening is forecast ON Saturday. So areas that don’t thaw Saturday could pick up another 1/2″ of ice glazing. That makes me think this could be a 1″ ice storm in East Portland east of I-205, assuming you folks don’t warm above freezing until late Christmas Eve (maybe well after dark). We will see. This European model forecast thinks all of Portland metro will be above freezing by Saturday morning. It’s warming us too quickly and doesn’t account for the extra freezing rain Saturday. But it’s producing plenty tonight through Saturday morning (when it thinks we’re done)

That’s it for now...I’ll be on TV all late afternoon through 11:30pm! And we’ll try to post updates to our weather app regularly this afternoon and evening too. We do have a separate weather app, in addition FOX12 OREGON news app. You can find it here:

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