Heat Wave Continues One More Day

July 29, 2020

8pm Wednesday…

One week ago I posted that our hottest weather of the year was on tap, evening mentioning a 100 degree temp was possible. It happened, and now we are in the middle of a heat wave across Oregon and the southern part of Washington. We actually do very well (as do models) with heat waves; I can’t think of a heat wave we have “missed” in at least 15 years. They are so easy to forecast compared to wintertime events with inversions, temps near freezing, and mixed precipitation types. PDX hit 93 today and the entire Willamette Valley reached into the mid 90s

A scorching mid-summer heat wave continues in central/eastern Oregon. Expect over 105 along the Columbia River from John Day Dam to the Tri-Cities. Hermiston has gone from 101 > 104 > 106 the past three days

Tomorrow the NWS is forecasting 109 at Hermiston, among the top 5 hottest values there. Just about everyone east of the Cascades, even up around 3,000′, will hit 100 degrees.

Hermiston hit 111 during the June 2015 heat wave so this won’t be an all-time record, but close. Why so hot? A typical summertime hot ridge of high pressure in the upper atmosphere; centered just about over the Grand Canyon region. Hottest air is east of the Cascades = less than 100 degrees for Portland. Plus with the upper-level ridge east of us we don’t get easterly surface wind like we saw Sunday.

Tired of hot weather? Good news is that marine air will surge inland tomorrow night and cool us back into the 80s. By Saturday the ridge is a bit weaker overhead too, but “heights” are still high enough for a very summery weekend in the Pacific Northwest.

Then an upper-level trough moves by just north of us late Sunday/Monday. That’s a big push of marine air, maybe a day only in the 70s Monday if we get lucky

In general this ridging seems to want to stick around for another 10-14 days. The result should be little/no rain through early August and temperatures near/above average. Check out the ECMWF ensemble forecast for rain. Each line in the top half of the image is one individual ensemble member’s rain forecast. The bottom half shows the average of all ensemble members. Yep, less than .10″ rainfall at Salem in the next two weeks!

How warm? After one more hot day tomorrow in Portland, we cool into the low-mid 80s and then around 80 next Monday/Tuesday. Expect at least some warming the mid-latter part of NEXT week.

To summarize…


Chief Meteorologist Mark Nelsen