By Mark Nelsen
Published: Aug. 28, 2023 at 7:01 PM PDT
What a change today!
A thick marine layer surged inland overnight and never left west of the Cascades. In the “before” times (pre-2013 summers), this happened at least once every week or two in July and August. Nowadays an all-day marine layer is rare as warm/hot weather is far more consistent most summers in a warming climate. At 6pm you can see the thick cloud cover west of the Cascades and over Portland (yellow dot), clear sky but thin smoke at Hood River (2nd yellow dot), then a hellscape of fire smoke arriving in Bend (3rd yellow dot). AQI over there is 200-400 right now!
We only hit 71 in Portland today, the coolest day in over 2 months. In fact just two weeks ago we had a LOW temperature warmer than today’s HIGH
Our 5th (and likely final) heat wave of 2023 ended up being 3 consecutive days at 94 in Portland; yesterday the marine air started to push inland and that kept us below 90
At this moment, August is still running the warmest on record in Portland at 76.1 degrees. The average HIGH temperature is in the upper 80s. I remember early in my career (25-30 years ago) it was assumed that as summers warm, Portland would have temperatures more like Roseburg or Medford experience (in the 1990s). Sure enough, our average high has been in the upper 80s this month. Assuming our 7 day forecast is accurate, August 2023 will probably still go down as the hottest month on record in Portland, just slightly ahead of LAST August!
Other stations in the region aren’t quite as hot; Portland’s nighttime urban heat island is becoming more and more pronounced as the decades go on. Regardless, another blazing hot summer month for all of us inland from the coastline.
WHY SUMMER IS SORTA “OVER”
The big thing that sticks out to me today is the lack of heat on models the next 10 days. Sure, it’s possible we slip in a 85-90 degree day sometime before the first week of September is up. But more likely it’s going to be feeling like September through the foreseeable future.
Here’s a forecast of 500 millibar height anomaly for the next 7 days (GFS model ensemble average). Upper level troughing wants to sit along the West Coast most of the time. This is a one week average. No hot ridging nearby to keep us in the 80s/90s. You can get a nice/warm/sunny day(s) in this pattern. But in general, west of the Cascades we’ll see showers from time to time in this setup.
Then check out days 7-14; looks similar doesn’t it?
What about rain? I see several upper-level “shortwaves” (smaller disturbances) moving through this big trough. One tomorrow, Thursday, early Friday, and another Sunday. Models are suggesting THIS THURSDAY COULD BE A SOAKER. Check out the 10 day rain forecast from the Euro ensembles. 1/2″ to 1″ in the western valleys, and 1-2″ in the Cascades. This will put a serious dent in fires over/west of the Cascades, especially combined with cool temps and higher humidity.
Looking at it another way, you see many chances for showers from the different ensemble members over the next two weeks. It appears the wettest period IS the first 7 days.
Then check out the forecast temperatures from just one model, the GFS ensemble average; quite pleasant don’t you think?
SUMMARY
- The endless stream of warm/hot/sunny days is over for the season
- Yes, but we’ll still see lots of warm weather (just not hot) the next 10 days
- Showers will dampen things at times, but I don’t see heavy rain for now
- This is NOT the beginning of the fall rains, that’s more typical later in September
- If you are tired of the blazing hot weather, enjoy the next 7-10 days!
One practical effect; my cheap above-ground pool may not get used again this season. The water temp peaked at 89 degrees during the heat wave and now it’s down to around 80 degrees. After the first week of September the low sun angle and long nights mean it just doesn’t warm up anymore. That’s even with a 90 degree day! Summer will be fading the next 2 weeks...
Copyright 2023 KPTV-KPDX. All rights reserved.
