Warmest Day Of Summer So Far, Plus More Summer Heat Ahead

June 21, 2021

8pm Monday…

We hit 97 degrees in Portland today, the hottest day so far this summer.

Recall that we hit 95 back on June 1st. Today was our 4th 90 degree day of the year.

Weak (and hot) easterly (offshore) flow continued through this morning, but now onshore flow (westerly wind) has arrived west of the Cascades. Temps are cooling nicely compared to yesterday, especially near the Coast Range where the cooler marine air is pouring through the low elevation gaps. This means our “mini-heatwave” has ended; tomorrow will be much more comfortable. In fact the next three days should be nice, just a little on the warm side

Keep in mind our typical high temperature this time of year is in the 70s, so we’re only “cooling” down to 8-12 degrees above normal this week. That’s because the hot ridge is weakening only temporarily…Here’s the Thursday map

Already a new ridge is popping up just to our west. But watch what happens by Saturday

A massive hot dome of air directly over the Pacific Northwest. For the geeks, 500mb heights are forecast to 594dm or higher. The 18z Euro ensemble average even paints a 597dm just north of us.

This is major heatwave territory

The big meteorological questions with 5-6 days to go:

  • How strong will the ridge be and where exactly will it be centered?
  • How high will 850mb temps go? Operational model runs are forecasting hottest ever recorded over Salem on Sunday (+30 to +31 on both GFS/ECMWF). Could that really happen? It’s never been above 28.3 there.
  • Will there be offshore flow…or weak onshore flow? That the difference between 102 and 108 (just an example)
  • How long will the hot ridge stick around?

For now, our 7 Day Forecast looks like this. Those numbers Saturday-Monday are a bit on the low side considering what we’re seeing on models:

I’ll get into more detail tomorrow as hopefully things become a bit more clear. For now…

  1. We have a heatwave coming next weekend. It’s TBD whether it’s a “typical” heatwave or something historic.
  2. Make your plans based on that information. If you don’t have AC…maybe head to the coast or Cascades?
  3. IF power goes out next weekend at your home, and you have a medical condition, what would you do? Start thinking about that.
  4. The all-time June temperature record (102) is in jeopardy at PDX
  5. This entire 2nd half of June is going to go into the history books as a scorcher, like 2015. Keep in mind today was the 6th day with a high temperature at/above 80 in Portland. There will be at least 7-8 more.

Chief Meteorologist Mark Nelsen