Beautiful Start To October, But Intrigue Lies Ahead…

Beautiful Start To October, But Intrigue Lies Ahead…

Columbia River Near Taylor Lake
Columbia River Near Taylor Lake
Credit: Karl Bonner

What a lovely start to October! Honestly, you couldn’t ask for much more perfect weather than this. Cold nights with patchy frost in some areas, and mild sunny days in the low/mid 70s in the lowlands. The airport in Dallesport dipped as low as 34 the night/morning before last.

I noticed a slight patchy frost on some car tops and maybe a hint on rooftops, this morning around 7:30am. But it was very subtle and there was no sign of any damage to tomato and pepper plants. I haven’t asked around, but I would imagine gardeners in any of the colder local microclimates – Mill Creek, Threemile, or any of the highlands – might have run into trouble. On the plus side: this kind of pattern, with cold nights and warm days, is excellent for triggering vibrant deciduous leaf colors. We should see them really start to pop, some time in the next 1-2 weeks.

We get one more nice day tomorrow Friday. Then a weak and cool system slides down the coast from British Columbia over the weekend. It will give only very light showers, to a few spots mainly west of the Cascade crest.

A couple days ago the plan was for another decent stretch of sunny and mild weather to begin next Monday for 3-4 days or more. But now the overall weather maps have shifted quite a bit. A strong and chilly (at least for this early in the season) Arctic High Pressure system builds over Alaska and the Yukon, toward the middle of next week. We get another “dive bomber” low by next Thursday into Friday, bringing cool showers down the coastline. It is followed by a very cool and dry Canadian airmass, with NNE wind and 850mb temps over The Dalles around -2 or -3, by next weekend.

This morning’s ECMWF run (12z) first showed the chilly air slipping into west-central Canada, by next Thursday afternoon:

ECMWF 850 hPa temperature anomalies

This actually looks a lot like a signature La NiƱa winter pattern, with cool showers in the Pacific Northwest and a dome of cold air over much of Canada. It’s very impressive to see that kind of signal set up for mid-October. It means much of Canada will get an early start on snow cover, which is crucial if you want to ‘conduct’ arctic airmasses southward later on.

In any case, the fresh 00z GFS, for NEXT Sunday morning:

GFS 850 temps and 6-hour precipitation ending 12Z Sunday 10/15/2017
GFS 850 temps and 6-hour precipitation ending 12Z Sunday 10/15/2017
Credit: National Center for Environmental Prediction

Wow…that’s one fine Canadian cold high pressure center! The airmass temps in the Columbia Basin are about -3. In mid-October that probably means a hard freeze at night, plus daytime temps only in the 50s despite full sunshine. So if the recent ECMWF and GFS runs are to be believed, we have some rather chilly conditions over us or near us, by late next week.

If this actually comes to pass, does it represent the beginning of a long and frigid winter for the Northern Hemisphere? We can’t really know. All I can say is that La Nina is now favored to develop this winter, and it usually favors colder and/or wetter outcomes. Especially later in the season, as in February-March. And Siberia is already getting cold in early October, with quite a bit of fresh snow cover in place. All of this works in favor of us getting colder and colder, as winter approaches…

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