While the national political weather remains as turbulent as ever (and hurricanes keep pounding the Gulf of Mexico!), Pacific Northwest weather has been quite boring by mid-autumn standards.  We had one minor windstorm last weekend in Portland with gusts up around 40-45 mph.  But there has been little else to talk about.

In other words, a perfect opportunity to take my mind off weather and focus on some other life goals.  I have a little bit of past saxophone experience but nothing like the French horn, which I’ve played off and on for roughly a decade total. I’m taking lessons from a sax teacher once every 2 weeks, and the homework requires me to practice about 1 1/2 to 2 hours every day!

….But after several busy weeks of scales, overtones, transcribing solos and going to jam sessions, something VERY interesting has popped up on the weather maps for late next week. More on that shortly.

Have you noticed something outside the last week- or rather, noticed the lack of something?  We’re into October 18th now, and there are very few colors on the deciduous trees in Portland!

That’s because September and October have been unusually warm this year- especially the nights. We have had only three nights below 50 degrees, so far at PDX this fall! September was about 3 degrees warmer than normal and the first 17 days of October, 4.3 degrees. And most of that has taken the form of balmy nights.

 

Normally we see our peak fall colors in the 3rd and 4th weeks of October, here in the city.  It’s obvious that we’re still at least several days away from the onset of peak foliage this year. Rest assured though…we have a pattern change coming the second half of this week, a change to much cooler conditions across the region.  And the festival of colors will arrive shortly thereafter.

The past week or so, models like the GFS and ECMWF were fighting over the long-range outlook:  does it stay mild and dry over the PNW, or does cold Canadian air start to come into play instead?  And then about 2-3 days ago…lo and behold, the models started moving toward the cold scenario. That happens when an upper-level ridge of high pressure and warm air builds over the Northern Pacific and Southern Alaska, allowing cold northerly flow to send arctic shortwave disturbances down the eastern flank and into the Pacific Northwest. This is the classic pattern for almost all our winter cold spells.

This morning’s 12z GFS is leading the charge most aggressively. It shows a pulse of cool North Pacific air arriving Wednesday. That brings a few light showers, with light snow likely about 4,000 feet in the Cascades; maybe a soggy inch or two at Government Camp?

That’s chilly, but not exceptional:  we would be in the 50s in the lowlands as opposed to the normal low 60s.  But then things get REALLY weird beginning Friday night. A low pressure center dive-bombs the West Coast, pulling down cold arctic air in its wake.  Here is the WRF-GFS 925mb / surface pressure map for Saturday morning :

Given that it’s the middle of the night with no solar heating at the surface, could we see LOWLAND SNOW out of this?  The model sure thinks so, showing heavy accumulations for the Gorge, Northeast Oregon, and lighter accumulations in NW Oregon:

If – and it’s a humongous IF with 6 days to go – this did come to pass, it would be a historic October snowstorm for NW Oregon, SW Washington, and the Columbia River Gorge.  This is followed by a few days only in the 40s, and wind chills likely 20s/30s!  Maybe even a couple days only in the 30s for The Dalles and Pendleton if there’s snow cover.

Now…the ECMWF hasn’t been nearly as exciting as the GFS – but recent runs are trending colder, if only briefly.  The 12z from today has the cool front for Wednesday and then a less aggressive push of cold air Saturday:

That’s still cold enough for some snow in north central Oregon, and maybe a soggy mix down to pretty low elevation in The Dalles and Hood River. But the cold airmass moves eastward much more quickly than on the GFS.  So we wouldn’t see anything too wild on the west side, though many locations could still get a hard freeze for a couple nights.

The Climate Prediction Center sure seems to want a cold/snowy outcome for the Rockies and Intermountain West,

next weekend and beyond.  Here is the outlook for Saturday the 24th through Wednesday the 28th:

 

Obviously, it’s dangerous to predict snow on the maps six days out.  We never know exactly which way the lows will meander, which makes a huge difference in this kind of pattern. I’ve seen these promising cold spells collapse on the models countless times, often only 3-4 days in advance.   The fact that it’s October and the GFS scenario has no good analog in my lifetime, gives me even more reason to be cautious.

Nonetheless, evidence on the models is growing that we have some kind of chilly pattern on the way, beginning about 3 days out and continuing at least through next weekend.  Whether it’s a typical fall cool snap or an unusual blast of early winter though…stay tuned over the next couple days as the forecast comes into focus.  The “moderate” scenario drops the lowlands into the 50s for a few days (maybe some 40s in the Gorge) and nights likely cool off into the 30s/low 40s.  The extreme scenario brings snow at least close to the Western lowlands, and we get some days only in the 40s with freezes at night in many areas.

So pay attention to the maps, and enjoy the mild temps these next 2 days.  -Karl