Wow…what a crazy 10-12 days it has been. Never before in my life as a WX geek, have I seen this much uncertainty & disagreement as to what’s going to happen 7 or even 3-4 days ahead in the forecasts.
WHAT’S BEEN GOING ON?
I’m not going to dig up a bunch of graphics, but remember that ridge / dry spell we had a week or two ago? Well this week the ridge “retrograded” a bit out into the Eastern Pacific and up into Alaska. Several days ago, quite a few of the GFS and ECMWF model runs showed a pattern favorable for some kind of Late December arctic blast across the Pacific Northwest.
Well…that ridge has moved too far north now on the maps, and there’s too much “undercutting energy” in the central Pacific. That means we don’t get a big arctic blast, but just some moderate cold air slipping into the Columbia Basin & Gorge.
That process should begin today Friday. Snow levels in the Portland area and West Gorge are already very low, below 1,000 feet this morning. There’s no precip in The Dalles right now. However, that could change this evening as colder easterly flow arrives from the north-northeast. I’ve seen it happen in The Dalles a few times before. The WRF-GFS shows quite a bit of snow to low elevations, between 4pm today and 4pm tomorrow:
The 3-hour images show most snow over north-central Oregon between about 8pm this evening, and 7am tomorrow morning. So if you live in the Gorge or just about anywhere east side, plan on seeing white in the lowlands for the first time tonight.
The bigger question is what happens Christmas Eve, after cold air has settled in and moisture tries to return. Some models were trying to give the entire Willamette Valley a snow/ice storm, but others are a bit more conservative with the supply of cold air. (Generally the further south the incoming storm track, the more that cold easterly flow will stay in place for them.) I’m not going to speculate exactly what happens in Portland…but for the central/eastern Gorge, it seems a second shot of snow is likely Sunday afternoon/evening.
The bottom line? Just about everyone in the Gorge from Cascade Locks eastward should see their first “real” snow of the season tonight. There will be a second wave of wintry precip on Sunday, but we don’t know precisely how far into the Western Gorge, Portland Metro, and Willamette Valley the frozen precip will get with that one.
Regardless, both Hood River and The Dalles should have snow on the ground Monday morning, making for the 2nd consecutive White Christmas for our region. Last year, we actually didn’t have a lot of fresh snow at Christmas, and the leftover snow we did still have partially disappeared for a few days just before New Years. As a result, 2017 will probably be the most magical-looking Christmas since at least 2012. Maybe even a bit more magical since it’s coming a day or two before.