So far this week has turned out about as expected. I made these points on Sunday (bold is what happened)
- Temperatures finally cool down to, and then below normal for late October this week. That’s going to be quite a change! In fact by next weekend it’ll be jacket/sweater weather (WE HAVE COOLED AND THIS WEEKEND LOOKS COLDER)
- First snow is likely in the Cascade Passes either Wednesday (less likely) or Friday night (more likely) (SNOW IN THE AIR YESTERDAY; AN INCH OR TWO STILL POSSIBLE LATE FRIDAY NIGHT)
- First frost is likely in outlying areas Thursday and/or Friday mornings (JUST HAPPENED THIS MORNING!)
- I don’t see a rainy weather pattern for the next 7-9 days, just some showers at times (ONLY .01″ SO FAR THIS WEEK, & ONLY A FEW LIGHT SHOWERS EXPECTED THE NEXT 7 DAYS)
- There is a small chance some lower elevations in the Gorge and eastern Oregon get a very rare October snow dusting late this week. (MOST OF THIS WON’T HAPPEN, MODELS BACKED OFF ON COLD A BIT AND MOISTURE TOO)
Today was the coolest day so far this fall…only 57 degrees in Portland. Not exactly a “chilly” day, but we get used to all the warm weather so far this month
Of course what was most noticeable was the morning chill and frosty areas. About 1/2 of the metro area saw a first frost today
Here in Portland we had an early frost last year, but most years we don’t see it until sometime in November
Right now a warm-ish area of upper-level high pressure is centered south and west of us. A cool upper-level trough moved through yesterday (remember a few showers?); that’s why we’ve turned cooler.
But look up to the north right where British Columbia, Yukon, & NW Territories meet. A pocket of cooler air is about to surge south. By midday Saturday it is swinging through the northern Rockies and Intermountain region
That’s chilly air for this early in the season. Ahead of it a Pacific frontal system brings us light showers tomorrow. Then cold air pours in behind during the day on Saturday. By that time most of the moisture for producing snow to lower elevations east of the Cascades is gone. That’s why I don’t expect any significant snow in the Oregon Cascades or most of Eastern Oregon. Notice the ECMWF snow forecast is quite “dry”.
You’ll need to be in the Blue or Wallowa mountains to get more than 1-2″ snow this weekend. Even there models have really backed off, because that upper-level system is shunted a bit farther east. By Monday, the warmer upper-level ridge is popping back up over us…lots more dry weather ahead!
What we WILL get over the weekend will be an increasingly strong easterly wind. This will be the strongest event since the Labor Day East Wind Storm. Models are consistently showing a 16-20 millibar gradient from Spokane down to North Bend (OR) by Sunday morning. The WRF-GFS tends to overplay the low level cold, but you get the idea. Lots of isobars = a very windy day Sunday for ALL areas west of the Cascades, not just near the Gorge. Here’s the WRF forecast for 5am Sunday…brrr! It may be tough to get above 50 degrees Sunday. Combine that with wind and it’ll feel more like late November or early December; for one day
The cross-section gives 50-55 knot wind (circled) Saturday night through early Sunday between 2000′-4,000′ over the Portland area. That’s not ridiculously strong like what we experienced Labor Day evening. But it’s strong enough to give us gusts 35-45 mph Saturday night through Sunday. Even though dewpoints will be plunging Saturday night, all that wind will keep us well above freezing. Sunday night should be a different story as the wind dies down. Very dry air, calming wind, low humidity…much of the urban area away from the Gorge will see a killing frost (down to 30 or so).
Much of next week will be dry. The ECMWF 15 day ensemble run from this morning…each horizontal line is one ensemble member. Time goes from now on left side to 15 days out on the right side. Highlighted is next work week.
So, much like last year it appears we’ll be seeing a slow start to the rainy season. Maybe a dry Halloween? We’ll see, that’s still 9 days out.
Enjoy the sunshine! After tomorrow’s showers…
Chief Meteorologist Mark Nelsen