December Is Here! Dry & Brisk Until Further Notice

December Is Here! Dry & Brisk Until Further Notice

It’s been quite a while since I posted last, but not too much of interest has happened since then. The biggest “story” was our record warm Thanksgiving in The Dalles, at 67 degrees F. We’ve actually had 3 of the last 4 Thanksgivings, turn out extremely balmy in the eastern Gorge. Don’t worry, I’m sure the more typical 40s will be back within a year…or two at most.

It’s been well-advertised on weather models for over a week now, but today was the first true day of DECEMBER DROUGHT ’17. That’s because we have an unusually strong and persistent upper-level ridge of high pressure, in the mid- to upper troposphere, that will set up shop along the U.S. West Coast through all of this week and next weekend. Possibly even a good chunk of next week. High pressure in the upper atmosphere generally means a warm dry subtropical airmass is pushing the jet stream northward, sending all the Pacific storm energy up into Alaska.

Here are three slides of the 12z ECMWF airmass maps from this morning. First for 72 hours, or 4am Thursday morning:

The ridge is locked in strong on the West Coast while the Central and Eastern U.S. get their first big cold blast of the winter season. Meanwhile, much of California and parts of coastal Oregon will enjoy “Riviera Weather” with tons of sunshine and temps well into the 60s and 70s.

Ridge is still holding strong by next Monday morning:

By this time the chilly stagnant inversion air in the Columbia Basin and southern Willamette Valley, should be getting very cold and dense. Indeed, by this weekend The Dalles may struggle to get above 35 degrees during the daytime, under the dark stratus clouds drifting in from the east. Meanwhile, anybody west of the Cascades and much above 1,000 feet, should be enjoying spring-like conditions!

Here’s the Euro map for next Thursday morning, fully 9 1/2 days away:

Notice the ridge has “retrograded” (moved westward) slightly, but still not nearly enough for any kind of arctic air to slip into Eastern Washington. You need the ridge axis to be AT LEAST another 10-15 degrees further west, around 140 to 145 W, before that scenario even begins to come into play.

As it is….there is essentially zero chance of any kind of cold upper-level airmass getting anywhere near the Pacific Northwest, any time in the next 10 to 12 days. There will also be virtually no chance of rain the entire time. That’s awfully unusual for what is normally our wettest month of the year!

As for the chilly inversion layer east of the Cascades? That means strong east wind through the Columbia Gorge beginning tomorrow and continuing at least through next weekend. Wanna go up to Corbett & Crown Point for some extreme wind tourism? Right now it looks like Wednesday morning might be the windiest of all, but just barely so. Thursday’s wind should be almost as powerful, and I plan to go that day since I have the day off work and wanted to go to Portland anyway. Here is the WRF-GFS surface pressure map for 10am Thursday morning; Wednesday looks very nearly identical:

That wind isn’t going anywhere for a while, and it should get progressively colder over the next few days as the low-level airmass in the Columbia Basin gets chilly.

So to sum up….We have an exceptionally dry and stable pattern on the way the next ten days, with increasing cool stagnant air in the lowlands. A bitter east wind in the Gorge will clear out the fog for Portland and NW Oregon, keeping them sunny most of the time. But due to the “source” of the wind (the Columbia Basin) being quite cold below 3,000 feet, I doubt that even the sunny places will get very warm. If anything…low humidity in NW Oregon / SW Washington means that away from the really strong Gorge wind, there will be the first solid freeze of the season.

It will be fun to track the temps over these next few days, especially across the greater Portland Metro where there will be varying amounts of Gorge influence. My Thursday trip should be a wonderful lesson in “Fake Cold Microclimatology”!

Meanwhile, the ski resorts and snow-loving weather nerds will have to wait a couple weeks for another chance.

Enjoy the sunshine and/or fog!

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