7pm Thursday…
Get ready for a real taste of October weather this weekend! Luckily that does NOT mean a ton of rain. Let’s just say it’ll feel a bit more “refreshing”.
Summary
- Nothing dramatic is expected (weather-wise) below 4,000′ over the next few days
- Cooler showers arrive Friday afternoon in NW Oregon and SW Washington. Then expect light showers off/on Saturday. Sunday might be dry west of the Cascades. There will be plenty of sunshine between showers the next few days, not gloomy at all.
- Coastal weather looks great! Not many showers Saturday OR Sunday.
- Temperatures drop well below normal for late September, but frost is unlikely for 90% of us west of the Cascades
- Light snow is possible down to around 4,000′ or maybe a bit below both Saturday and Sunday mornings. Trace-2″ at Government Camp, but possibly 6-10″ up at Timberline Lodge by Sunday afternoon when things dry out
- Passes should remain clear, although a brief morning dusting or icy spot is possible both Saturday and Sunday mornings.
This weather pattern has been forecast quite well by our weather models. For the past week they’ve been showing a cold pool of air dropping south through western North America. Sure enough, this evening a cold “upper-level trough” is right over Juneau, AK
By Friday afternoon it is right over Washington, this IS our “arctic outbreak” pattern in winter.
Then by Saturday afternoon it’s over NE Oregon. A large upper-level ridge has developed in the eastern Pacific and cold northerly flow extends from the Yukon down to California!
We get a surge of showers ahead of it Friday afternoon and evening, then the majority of shower action Saturday evening and beyond moves south and east of us. At the same time high pressure at the surface turns our wind flow “offshore” late Saturday. That gives us an easterly wind Sunday and Monday, drying things out with plenty of clearing.
The WRF-GFS (from UW) cross section over Portland shows the big cool down in the airmass overhead. Time goes from right to left, starting with this morning and ending on the left side with Sunday afternoon. I’ve drawn the zero degree line (celsius) in blue. The 850 horizontal line is around 4,000′. You see it goes from around 50 degrees (F) at that elevation today to about 32 degrees late tomorrow night. It remains within 5-10 degrees of that freezing mark through at least Monday morning.
That means it’s reasonable to say anything above that 4,000′ elevation will fall as snow beginning sometime after sunset Friday. Models are showing plenty of mountain precipitation tomorrow night through Sunday morning. I see the 18z ECMWF is giving the higher parts of Mt. Hood 6-10″+. That seems reasonable. Same thing in the central Cascades of Oregon and at least 2-6″ in higher parts of Eastern Oregon too.
Our RPM model thinks there will be spots over 10″ up around Timberline and higher. Seems reasonable and goes with the Euro forecast
There are even hints that at least a dusting could fall down to Sisters, Bend, and Redmond by Sunday morning with a cold northerly wind blowing moisture “upslope” into that area. This is a classic hallmark of an “arctic blast” in that area. Northerly flow moves uphill from the Columbia River into Central Oregon, clouds form, and snow is squeezed out when the air rises. We don’t get many situations with flow from that direction but it’ll probably happen over the weekend.
The big snow/cold event will be to our north and east. Look at all the Winter Storm Watches and Warnings across Washington, Idaho, & Montana. Some spots in the Rockies could see 3-4 feet of snow! Very early, even for that area.
So how “cold” will we get in the lowlands west of the Cascades? For most of us Sunday will probably be the coolest day. Even with abundant sunshine we’ll barely make it to 60…maybe only upper 50s
If you’re a gardener like me you might be worried about frost. I think that’s unlikely for most of us west of the Cascades. Maybe either Monday or Tuesday morning around Tillamook, Vernonia, Banks, Battle Ground. Just the very coldest outlying areas. The rest of us remain above 35 degrees. Your warm weather veggies won’t like it, but it’ll sure give them the hint the “end is near” for this growing season.
What you’ll notice most Saturday through early next week will be the refreshing air and bright sunshine and of course much cooler mornings.
Enjoy your weekend! Chief Meteorologist Mark Nelsen
FOX 12 Weather Blog 
This September has been awesome. Crazy thing is that we are still above average temperature-wise. Again due to warm overnight lows.
Snow on the trees and a dusting in the grass, North end of the Warm Springs plateau.
And it’s snowing. Road is wet.
Elevation 2,500 ft.
Took the kids up to play in the September snow yesterday. There was a solid 6” up by Bennet Pass, 4700’. Was a great family day with my dog Reload who turned one yesterday. This weather is the way Oregon needs to be, absolutely love it.
Another cold upper trough shown on models for October 7-8. This time is a much stronger cold front…could be some wind damage in north of Puget Sound. Looks like a strong Puget sound convergence zone too. Front should be impressive here in Oregon as well. Too early to say if convection will be with the front but it looks likely postfrontal.
Nice sized cell rotating just north of me. Hearing thunder every minute or so.
Just had a heavy graupel/hail shower come through to the North of Madras, dusted everything white for a few minutes, including the pavement on Hwy. 26. Splat test absolutely positive.
Elevation 2,100 ft.
Gonna be chili there for a few nights. Hope you got your woolies with you!
Had the fireplace in the cabin stoked up so hot, practically turned the darn thing into a sauna! 😂🤣
…i never thought i’d be saying windshield splat test is positive in september…..but it is and i am!…tonight and tomorrow are going to be real interesting over here…
Hey Larry, we moved to the south coast of Oregon. If you ever think you need a place to be a camp host and you want some relief from the cold….check it out.
Heavy showers here early last evening, after what had been a mainly sunny but windy day. This September will end up as my second wettest in history.
That tsin and 20 mph crosswind didn’t stop me from a 50km on the bike. A nice refresher though but it could’ve waited 3 months
Anybody know how they were able to see this arctic type front or low originally coming? I couldn’t see any evidence of it in the early stages when first mentioned. So I’m impressed…… how does Mark know do that?
The sig you should have been looking for was the massive retrograding ridge that pushed up into Alaska. That always displaces the cooler (cold) Arctic air and pushes it South and East. Depending on how far to the West that ridge moves will determine how far to the West that displaced cold air will drop. If the ridge is too close to us (as is typically what happens) then all the cold air gets shunted down the backside of the Rockies (as is typically what happens.) Every now and then we get lucky, as the ridge slides far enough away that the cold drops down into the PNW, like now. If this were anytime between the end of November and the end of March, we’d probably be seeing snow in the Valley and sub-freezing daytime high temperatures. But no, this is merely the beginning of Fall, so no such luck.
It would be nice if this pattern would hold and recur throughout the winter!
Heading to Madras this weekend, staying in a small cabin along the Deschutes. Hoping it doesn’t end up too snowy/cold…
So nice this morning – was 45 at my place! Cooler temperatures, some rain and some sun – great fall weather!
Hoping to see some snow fly this weekend as I am now in Culver.
Too bad we couldn’t get that historic snow that’ll hit the Montana Rockies. That’d be a great start to the ski season. This weather pattern is fantastic though. New property in S. central Oregon will get into the teens by the weekend.
The temperatures always moderate due to the mountains blocking the lowest, coldest air. It’s just that the super-cold air in Montana will bottom out around +20F this time, instead of -30F like it does in December or January, so the temperatures it will moderate to are also correspondingly warmer.
I’m just as glad I don’t live someplace where it can snow in late September, because those are the same places that get into the deep freeze for weeks on end in the dead of winter. You can always drive up to Timberline Lodge on Sunday (I may drive to Artist Point on Mount Baker this weekend just to see the snow myself).