I hope you all had a happy Halloween these past few days. I enjoyed a weekend stay in Portland, where I attended my first-ever OMSI Winter Weather Conference and got to meet several of my online weather buddies in person! Then by evening of the next day I was back in White Salmon, to celebrate the pagan festival of Samhain, which is a rough ‘ancestor’ of the modern Halloween.
It was a very warm end to October, at least for Portland and the Willamette Valley. Probably just about the warmest and sunniest pre-Halloween week possible for the climate of NW Oregon. But The Dalles needs light west wind, at this time of year, in order for really warm temps to show up at the surface. (In an easterly or northeasterly pattern the air can actually cool a bit as it passes through The Dalles, and begins to bump up against the slopes of the Cascades.)
On Halloween Night this exact phenomenon happened: between 5:20 and 5:35pm, just as the sun was beginning to go down, the temps at DLS airport suddenly jumped up by 8 degrees F, from 59 to 67, as a west wind suddenly arrived. It then stayed above 60 until after 9pm…and never got below 55 last night! Dewpoints briefly crashed into the teens when the wind started in the evening…then slowly rose back to more “normal” levels by morning. Obviously some downsloping going on as October ended and our early November pattern began to roll in.
Here are the basics as we move through the first week of November:
1. It’s definitely going to get much cooler and a bit wet across the Pacific Northwest, these next several days. In fact I think we may be done with 60-degree weather for a long time…this might be one of those years when we don’t have a single 60 between now and mid-March.
2. Snow levels in the Cascades will come down to between 2,000 and 4,500 feet Thursday-Sunday as a very cold early-season arctic airmass plants itself over Western Canada. This will dig a trough over the Pacific Northwest, spinning up a couple of weak disturbances.
3. Some model runs (especially the WRF-GFS) have shown a decent amount of cold, low-level northeasterly flow slipping down through Eastern Washington and into the Columbia River Gorge on Sunday – combined with moisture from a surface low moving by to our west and south. This is a “classic” pattern for snow in the Gorge in the wintertime, but on the 5th of November it’s going to be a tough call.
Here is the only map the wishcasters really “care” about, the 925mb map for the 12z UW WRF-GFS:
Those are temps as cold as -4 or -5 degrees Celsius (about 23-25 degrees Fahrenheit) just a little more than 2,000 feet up in the air over The Dalles and Hood River! If steady precip were to fall into this kind of airmass it SHOULD fall as snow all the way down to river level. But…the WRF-GFS is often notorious for overdoing cold air in these kind of “back door” events. Sure enough, here is the crazy snow forecast map through next Monday morning:
That’s gotta be the biggest snowstorm ever for the first week of November! Weather experts learn to take these models with a grain of salt, because their topographical precision isn’t very good.
Still….it’s possible that very late Saturday night or Sunday morning, there is some kind of rain-snow mix down to low elevations in the central and eastern Columbia Gorge. And with easterly flow undercutting incoming moisture like that….I doubt we get much above 40 degrees during the daytime on Sunday either.
We don’t know for sure what will happen until almost the evening before…so stay tuned to the forecast and the news for upcoming details.