The Great 2015 Northwest Heat Wave; A Historic Weather Event

July 5, 2015

We are suffering through the longest heat wave we’ve seen in at least 75 years west of the Cascades.  Does it live up to the title billing of THE GREAT 2015 NORTHWEST HEAT WAVE?  I feel that’s definitely a YES in the lower elevations of SW Washington and NW Oregon.  Likely it’s the same in many other locations as well.

I had a lot of free time this evening since it’s a Sunday and we only have one show at 10pm.  So I took an hour and looked over past records for the Portland area.

Where the heat wave stands right now

  • Today is our 7th consecutive 90 degree day in Portland (all-time record is 10 days from 2009)
  • Today is the 5th consecutive day at/above 95 degrees! (not a record, we’ve seen 5 100 degree days in the past!)
  • 10 out of the last 11 days have been at/above 90 degrees
  • Today is the 14th day this summer above 90 degrees (we’ve passed our yearly “allotment” on July 5th)

* Note I’m calling this a heat wave (singular) because of the duration.  We only ended up with one day down at 85 degrees.  Looking back I’m quite confident we’ll look at it as one long event.

Our 7 Day forecast looks like this right now:

7 Day

Note that we PROBABLY have 4 more days in the 90s before the well-advertised cooldown at the end of the week.

Assuming we stay above 90 degrees as forecast, by Thursday evening it should look like this:

11 consecutive 90 degree days (A NEW ALL-TIME RECORD)

14 of 15 days reached 90 degrees or hotter (Unprecedented in Portland history)

18 – 90 degree days for the season…ALREADY BY JULY 9TH!


I have looked all the way back to 1940 in airport weather records (official observations) and can not find a similar duration of hot days; or anything close to it!  Now add the fact that warm overnight lows have been breaking records right and left (6 tied or broken so far).  This is a truly historic hot weather event for our area.  Not the hottest heat wave we’ve seen, but the longest.

Remember our “greatest heat wave” in 1981?  Yes, 4 days at/above 100 culminating in a 107 twice!  Or the July 1941 heat wave when we were above 100 for 4 days!  Even in those events, cooler weather (60s-80) preceded it or followed soon after.  This time it’s just been one long continuous warm spell.

There are two heat waves that attempt to come close to this one…

JULY 1985:  10 days 85+, but no more than 3 consecutive days above 90 at a time.  22 consecutive days;  only 2 were below 85!

AUGUST 8-22, 1967:  8 days 90+, 15 days 85+.  But all nights were 60 degrees or cooler…much more comfortable

By the way, you may be thinking of some other heat waves.  Wondering if I missed your favorite?  Here are 2 others that were quite impressive.

JULY 2009:  10 days 90+, then quickly down to 60s/70s for highs!

AUGUST 1992:  A hot month, 10 days 85+, but cool just before and after

AUGUST 1972: A hot 10 days, 7 days 90+, but cool just before and after like 1992

Have you noticed one thing has been missing?  No 100 degree days (in Portland).  In fact we haven’t been above 97 which is very strange for such a long period of hot weather.  This is the 2nd summer (so far) in which we are not seeing sharp thermal low pressure troughs develop west of the Cascades; sending a hot east wind down into the valleys.  That’s when we go above 100 degrees.  Those are often followed by a dramatic cool down as well.  Interesting that we’ve had upper-level highs consistently over us for a hot atmosphere both years, but very little amplitude to the flow to give us brief offshore flow.  We’ve been doing much of this heat with weak-moderate onshore flow.

So you’re sick of the hot weather and wanting a cooldown right?  I think most of us are. We definitely have one for next weekend, but it remains to be seen if it’s just a brief cooldown and hot weather returns the 2nd half of the month.

Chief Meteorologist Mark Nelsen