Thick Smoke = Cooler Today, Back to Hot Tuesday

August 20, 2018

10pm Monday

Fire smoke had no problem moving down into northern Oregon last night and this morning.  In fact it was so thick (shadows barely visible at midday) that we were COOLER instead of WARMER today.  Lower 80s were the rule in the western valleys of Oregon and SW Washington

Todays Observed Highs OrWa 2017

What about tomorrow?  I think temperatures will soar quite a bit higher for two reasons.

  1. We had weak onshore flow today, but pressure gradients are switching now and we’re headed into one day of gusty offshore easterly wind tomorrow.  That alone would raise our temps 5 degrees or more.
  2. There are strong hints from the HRRR smoke modeling that smoke will thin significantly tomorrow afternoon.  That’s due to the strong easterlies bringing clear air from Montana westward all the way to the Cascades and beyond.  Check out the current smoke forecast for right now; widespread thick smoke across all of Oregon and Washington.  Much cleaner air just across the border in Canada.


Then the view at 5pm tomorrow after almost 24 hours of easterly flow


Look at that punch of cleaner air moving through much of Eastern Washington and right down into NW Oregon.  NASA’S GEOS-5 model shows a similar situation with smoke thinning the next 24 hours.

So the current air quality readings might improve quite a bit in the metro area and Gorge tomorrow afternoon.  At this moment it’s just as bad as we saw during last week’s smoky period

AirQuality Western Oregon

Looking ahead, it’s very obvious we have a sharp turn towards fall-like weather beginning Thursday.  It’s not that we’re suddenly going to turn rainy with highs in the 60s, but there’s no sign of a return to 90s or even 80s through the end of August (just 10 days away).

Check out the ECMWF ensemble chart for 850mb temps for the next two weeks.  Very good agreement that we’re headed into a much cooler period.  The green line is the average temperature at that elevation around 5,000′.  Notice most of the time Thursday and beyond the forecast temp is below that line.  Red is the average of all the ensemble members.  If this is the case, we’re done with the endless warm-hot days of summer and headed into a early fall pattern.

tseries_850t_000-360_Portland (1)

Unfortunately at this point I don’t see a good chance for a big soaking…the ECMWF average rainfall for this entire period is less than 1/2″ of rain.  Still, this weather will put a damper on fire behavior…baby steps toward the approaching wet season.

As for temps, you can see the stark change from Wednesday into Thursday as onshore flow kicks in and temps lower


I’ll be off the next few days, but back at work Sunday.  Things should look quite a bit different by then.

Chief Meteorologist Mark Nelsen