10pm Sunday…

Today was very mild with just a few showers, continuing a “dull weather” theme we’ve seen lately. Temperatures are running well above normal this month, partly due to warm nights. We’ve only seen one cooler than normal day so far this month (last Thursday). We’re running over 4 degrees above average for October, but of course we still have 13 days to go. Check out central and eastern Oregon!

If we combine the warm September with this month so far, the numbers are record or near-record breaking warm. Meteorologically fall began on September 1st (arrived about 10 days later for us in the middle of the cool/smoky period). Right now Portland is running 2nd warmest on record, just like Astoria to the west and Olympia up north. It’s the warmest fall on record (so far) at Redmond

But the main weather message for the upcoming week is…COOLER. We’ll finally see some cooler than average weather after tomorrow and maybe close to record cool next weekend.

Right now we are in a mild westerly flow coming over the top of an upper-level ridge offshore. It looks like this up around 18,000ft.

But several weak weather disturbances gradually “carve out” a cool upper-level trough Tuesday-Thursday. Looks different by Wednesday doesn’t it?

For the first time this season we’ll see cold air drop south out of Canada. Snow will fall down around 3,000′ in this setup, possibly bringing the first snow of the season to Government Camp and surrounding ski areas. Except there isn’t much moisture available. Maybe a dusting to an inch up at Govy later Wednesday through early Thursday, but it sure looks wintry north and east of us doesn’t it? Lots of cold air in southern Canada and into the USA Rockies

As dry and cooler air filters south Thursday & Friday, expect much cooler nights for all of us. First (and overdue) frosts are likely everywhere except in the cities west of the Cascades and along the coastline. High temps fall into the mid 50s even with some sunshine.

The most interesting event showing up on models occurs Friday evening through Saturday morning. Both the GFS & ECMWF models show some variation of our typical wintertime “snow storm setup” in Portland and the Gorge. That’s when a surface low pressure system comes down the coastline, pulls cold/dry air air out of the Gorge, and throws moisture over the top of that. Of course it’s extremely early for this setup and everything would have to be perfect for snow to fall to sea level in this pattern. The very reasonable ECMWF looks like this late Friday night

Low pressure is moving onto the Oregon coastline. A gusty east wind is pulling cold air down through Eastern Washington and through the Gorge. Yes, the ECMWF is producing snow in the eastern Gorge and down into Central Oregon.

Snow has fallen as early as October 26th in Hood River (5″ in 1919), and the 29th in Madras. The GFS model has been unrealistically cold plus wet the past few runs, so I discounted it. But this evening’s run is looking a bit more like the Euro (more reasonable). I’ll be keeping an eye on it all week, but in summary

  1. 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
  2. First snow is likely in the Cascade Passes either Wednesday (less likely) or Friday night (more likely)
  3. First frost is likely in outlying areas Thursday and/or Friday mornings
  4. I don’t see a rainy weather pattern for the next 7-9 days, just some showers at times
  5. There is a small chance some lower elevations in the Gorge and eastern Oregon get a very rare October snow dusting late this week.

Chief Meteorologist Mark Nelsen

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