Heat Wave: Confidence Growing We Will See Hottest Temps On Record In Portland

June 24, 2021

9pm Thursday…

This is just a brief post because NOTHING has changed meteorologically with the weekend forecast. All the points from yesterday are still valid. Just a tweak here/there


  • What will likely be the hottest heatwave on record in the Portland area (and much of northern OR/southern WA) arrives tomorrow and continues through Monday. And there’s a good chance we remain at/above 90 the rest of next work week.
  • Expect three 100+ days in Portland, and they may all be 105+
  • I’m very confident we’ll hit 106-108, and think 110 is quite possible for the first time here. Records go back to the late 1800s both at the airport and Downtown.
  • Humidity will be mostly reasonable…it sure won’t be “Bourbon Street Humid”, more like our typical heatwave humidity.
  • Overnight lows will likely end up warmest on record in Portland too. Low-mid 70s Sunday and Monday mornings. That means homes/apartments will remain dangerously warm with no chance to cool off. Typically we see reasonable overnight temps in our area.
  • The only place to cool off will be the coastline…more like 75-90 out there over the weekend. Most likely you won’t be alone if you want to play on the beaches. There’s a chance the far north coast makes it to 90 on Sunday…we’ll see.
  • I do not expect any sort of strong wind anywhere in the Northwest. BUT, some easterly wind will be felt over the metro area Sunday. Gusts 20-30 mph are possible. Enough to move an accidental fire along, but not enough to drop powerlines into trees.

I didn’t change any numbers for the weekend in today’s 7 Day Forecast, although we “overachieved” today with highs right around 90 in the metro area. I was thinking more like 86-87.

That boosts confidence in our extreme forecast numbers. Today’s forecast

850mb temperature forecasts remain the same (temp around 4,000′ overhead in Celsius). In fact, while making the forecast, I noticed both GFS & ECMWF ensemble averages matched through Sunday! +19 tomorrow, +25 Saturday, +29 Sunday (new record), +25-27 Monday PM. The only disagreement is over how quickly the upper-level low to our southwest Monday slides north offshore. Quicker movement Monday would lead to an earlier marine push = cooler high temps. Slower movement gives us another extreme day Monday. The most recent ECMWF ensemble average temps for Portland (near sea level) are just amazing. We were a few degrees warmer than forecast today. As I mentioned last night, we see that with Euro surface forecast temps in the warm season. That’s why we’re going 96 for tomorrow. Since the numbers turn so extreme Saturday-Monday, I’ve stuck with these numbers instead of going higher. I couldn’t imagine forecasting 111-114 for Portland…so I didn’t.

Check out the fresh 00z IBM Graf model, which handles warm season temperatures well. 108 Saturday, then around 114-115 Sunday! Just like the other models.

I’ve haven’t noticed this model “over-forecasting” heat in the last two warm seasons. Part of the reason we’re seeing such extreme temps (other than sun, offshore flow, and hot airmass overhead) appears to be the surfacing of that very dry subsiding air below the upper ridge. Notice the dewpoint drop both weekend afternoons. Sunday that would be relative humidity in the teens. The icing on the cake is the easterly wind Sunday. The GRAF is forecasting east wind to surface throughout the metro area that day (but not so much Saturday). It’ll be a “dry” 110 degree heat as they say…

In case you are wondering, the coastline WILL be cooler through this event. This applies to the northern Oregon and southern Washington coast…take off 5-8 degrees for Lincoln City and Newport

A few more numbers for you this evening. Portland’s all-time warm low temps. These are from the airport. With such a hot airmass, plus a larger metro area, plus a warming climate, it’s fair to assume we’ll be warmer than this.

This is dangerous for medically fragile or elderly folks…if you know any, please check in on them regularly!

That’s it for now, I’ll be on-air and online through NEXT Friday, the 2nd. I was already scheduled to work this weekend which is convenient. Make sure you are following me on Facebook: @marknelsenweather and Twitter: @marknelsenKPTV. I will be updating those much more frequently than this blog. 

Chief Meteorologist Mark Nelsen