For the past several days, there has been much speculation about the upcoming heatwave for the last weekend of June.  Would it be just “really really hot,” or would this prove to be the MOTHER OF ALL HEATWAVES for the Pacific Northwest?

Now, two days before the event begins, we appear to have an answer:  Yes, the June 2021 heatwave will probably be the hottest temperatures that northwest Oregon and SW Washington have ever seen (at least in the last couple centuries).  And the forecast for the Columbia Basin to our east is truly terrifying.

I’m not going to go into a detailed blog here; I have lessons and jam session tonight to attend to.  You can read excellent blogs by Charlie Phillips  and Mark Nelsen on the nitty-gritty.

WHAT’S UP?

In the middle of last week, long-range models began hinting at a HUGE heat event for the Pacific Northwest for the last weekend of June. Initially most weather geeks laughed; we’ve seen insane model rides with arctic cold before and this looked equally absurd in the hot direction. But here we are, less than 96 hours from the first of the “insane” heat days – and forecasts are refusing to budge.

Check out this ECMWF map from last night’s 00z to begin with:

This is the 850mb map for late Sunday afternoon. It shows temps around +29C for Portland and above +32C in southern Oregon!  To put into context, the all-time 850mb record for Salem Airport is 28.3C.  Also, the “heat dome” extends all the way up into the Northwest Territories in the Canadian Arctic! I’ve never seen a map this extreme before.

Here is the map by Tuesday afternoon:

HOLY CACTUS!  Airmass of +32c all the way into northern B.C.?  Portland will actually be slightly “cooler” by Tuesday with onshore flow, but east of the Cascades?  Easily the hottest on record.

We can turn to the 12z GFS surface maps to get an idea of the temperature.  First Saturday, the first triple-digit day for Portland:

Sunday and Monday are showing mid 110s for Portland!  Then on Tuesday as the “core” of the heat settles to our east, the Lower Columbia Basin soars into the low 120s!!!  I don’t know if that’s really going to happen though. For now I’d feel more comfortable forecasting 110 for Portland and maybe 115 next week for the Tri-Cities.

A couple thoughts:

1.  The all-time 850mb record for Salem (28.3c) happened in early September 1988.  As I recall Portland’s high temperature that day was 105F.  And that’s with far less daylight and sun angle than we have in late June!  So even if we just manage to equal the 1988 airmass, we’ll be looking at AT LEAST mid-100s for PDX, and possibly hotter.

2.  Drought will contribute to extra heat.  The drier the ground is, the easier it is for that group to heat up (or cool down for that matter).  And Oregon and Washington are in a massive drought right now.  I bet our high temps end up 2-4 degrees hotter than they would be under more normal soil conditions.

3.  Charlie, in his recent blog, suggested that our higher latitude would be a limiting factor on our temperatures.  It’s true that the sun angle here is about 12 degrees lower than it is in Phoenix, and 10 degrees lower than Las Vegas. But as you go north in summer, the days get longer. This “daylight effect” can offset the “sun angle effect” to a significant extent, especially near the summer solstice (right now!).  The main reason high latitudes don’t get as hot in the summer,  is that extremely hot airmasses rarely get that far north!  But this one is.

The ensembles for the 12z GFS are showing pretty good agreement for record heat Sunday and probably Monday.  Here for Portland:

The operational for The Dalles is anomalously hot after Monday; a sign that some of the forecast members want to bring a faster cooldown next week. So those 115-120 temps in the Columbia Basin are still tentative at this point.

THE FORECAST

Friday will be the first hot day in Portland. This will just be a “regular” hot, likely in the 94-97 range.  On Saturday the first of the crazy heat arrives.  Current models suggest a high somewhere around 105 or 106.

Sunday and Monday will be the hottest days Portland has ever experienced.  Expect high temps somewhere in the vicinity of 110 both days – UNLESS we get lucky Monday and  onshore flow starts early,  in which case we may “only” reach 100-105.  Then we return to “garden variety heat” Tuesday and beyond (i.e. 90s).

The Columbia Basin and eastern Columbia Gorge should be similar to Portland Saturday and Sunday. If operational maps are to be believed though, the most extreme heat will be Monday-Wednesday next week.  High temps will be deadly hot, possibly 115 or above.  Triple-digit heat is expected to persist east of the Cascades through all of next week. 

Obviously, I hope you are preparing for this heat wisely by canceling strenuous activities, stocking up on water and survival food in case the power goes out, and installing A/C units if you don’t have them.

Stay safe! -Karl