First heatwave of 2022 will likely feature a 100 degree day in Portland

Published: Jun. 24, 2022 at 9:23 PM PDT
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Today was nice with a high temperature of 84 in Portland, but now the heat sets in this weekend.

Our weather forecast models are in agreement that a 100 degree day is becoming more likely in the Portland/Vancouver metro area Sunday. All the factors that can push us to that century mark appear to be in place for just that one day.

For those just wanting the details:

  • Hot weather arrives tomorrow and sticks around through Monday along the I-5 corridor in western Washington and Oregon
  • Expect low 90s tomorrow and Monday, but between 98 and 102 on Sunday. Skies will be sunny all three days
  • Breezy and dry east wind keeps humidity low both tomorrow and Sunday, although it might get a bit more humid (briefly) Monday
  • A breezy west/southwest wind arrives Monday evening along with a major push of cool Pacific air. Tuesday we’ll be in the 70s most of the day!

Our 3 day forecast for Portland looks like this:

(kptv)

Along the northern Oregon coastline, the forecast (as always) is a bit more tricky

(kptv)

That warm/hot easterly wind touches the beaches tomorrow, but then really pushes in Sunday. When that happens, it CAN be just about as hot at Astoria, Cannon Beach, & Tillamook as it would be here in the valleys. Thus the 90 degree possibility.

Here’s the plan for the next 3 days...

A “thermal trough” of low pressure is developing west of the Cascades right now. That’s because low pressure forms on the “lee” (downwind) side of mountain barriers as wind crosses it. Easterly wind has developed over the Cascades and now air is moving toward that blue line west of the Cascades down here at sea level. Easterly wind is blowing at Vista House in the Gorge. This is the classic signature of an approaching heat wave west of the mountains. Notice wind is still weakly onshore at the coastline.

(kptv)

By tomorrow afternoon, a strong thermal trough is in place west of the Cascades, centered over the Coast Range. Temperatures warm a bit at the beaches, but really skyrocket inland. 4 millibars worth of pressure difference between The Dalles and Portland means a gusty easterly wind in the western Gorge. High fire danger...BUT...all the vegetation is very green out there...for now.

(kptv)

Then check out midday Sunday. The thermal trough has broadened and is right over the northern Oregon coastline. Hot east wind is making it to the beaches in that area. 4-5 millibar pressure gradient remains over the Cascade for a continuing easterly wind. But also notice the cooling southwest wind has arrived on the central coastline. It WON’T be a hot day from Lincoln City southward Sunday.

(kptv)

Finally, by late Monday afternoon (5pm) things have really changed. The thermal trough has shifted east of the Cascades with a strong west-southwest push of marine air in progress everywhere west of the mountains. A westerly gradient of 5-6 millibars means a very strong west wind has returned to the eastern Gorge. Big afternoon for kiteboarders out there! It’s possible that from Salem south temperatures remain below 90 on Monday.

(kptv)

These images are all from the high quality WRF-GFS model from the UW. The cross-section product is excellent for showing us the deep easterly flow tomorrow and Sunday (area shown in yellow), then the switch to onshore flow Sunday night. Easterly wind is blowing almost 50 mph over Portland (overhead) tonight and tomorrow night. Note that time goes backward on this graphic

(kptv)

That does keep our humidity low through most of this event. Dewpoints may briefly come up to “normal” for summertime Saturday night, but that’s about it. Dry stuff = good.

(kptv)

Models are now pushing 850 millibar temperatures (temperature in Celsius ~5,000′) to +23 or +24 over Salem Sunday afternoon. There have been two previous events just like this one in late June. Temperatures were similar overhead in June 2006 and June 2017. Both produced 100 degree days in Portland. And the setup Sunday afternoon is “perfect”. Easterly wind dies down to almost calm at peak heating time in the metro area, but cooler southwest wind hasn’t arrived yet. Totally sunny skies uninhibited by high clouds too. This all adds up to a 100 degree day.

That’s it for now, find a place to stay cool this weekend, and be careful on our local lakes and rivers.