A comfortable July so far, but heat wave #2 arrives early next week

Published: Jul. 20, 2022 at 8:54 PM PDT
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Today was a bit hot...for the 2nd consecutive day we made it above 90 degrees in Portland. That’s the 7th day so far this summer

(kptv)

You see the typical cool beaches and very hot east of the Cascades in the daytime highs

(kptv)
(kptv)

Tomorrow should be cooler as the hot upper level ridge just to our east shifts farther away, plus a weak system passes by overhead. The combination of these two has started a “marine push” of cooler air through the Coast Range gaps and up the Columbia River. The result will be patches of low clouds tomorrow morning inland and temperatures remaining in the 80s. A stronger push tomorrow night makes for a refreshing day Friday; there’s a decent chance we don’t get above 80 degrees that day...quite nice! July has been near normal in our area, but very warm across a good chunk of the USA. Note that this graphic is a few days behind.

(kptv)

But we have a heatwave ahead folks! Next week will feature the hottest stretch we’ve seen so far this year, and I give it a 50/50 chance this could be the hottest of summer when we look back.

HIGHLIGHTS

  • Comfortable weather returns the next 3 days
  • Sunday turns hot, about like today
  • For at least 3 days (Monday-Wednesday) temperatures will be up around 100, plus or minus a couple of degrees
  • There’s a decent chance we make it to 100 in Portland/Salem/Eugene
  • There’s a much smaller chance we make it to 105 in one of these I-5 cities.
  • We don’t expect an extreme heat wave

Why so hot?

A strong upper-level ridge builds right over the West Coast AFTER a cool system passes nearby tomorrow through Saturday. Over the past few days models have been in some disagreement on the strength of the ridging. Would it be a huge “heat dome” with upper level heights over 594dm at 500 millibars with high temps well above 100 degrees (ECMWF/GEM)? OR, just high heights with general ridging...high temperatures 90-95 degrees (GFS), nothing too unusual. Luckily models have come together much better today. The Euro has cooled, and the GFS has warmed. 500mb heights on Sunday are rising, very warm, but no big ridge over us.

(kptv)

Then on Monday afternoon heights have risen a bit more. A ridge is building over the Gulf of Alaska, and most of the USA is covered by a hot/flat ridge

(kptv)

By Wednesday afternoon the two have linked up into a hot ridge right through the Pacific Northwest. Heights around 591dm

(kptv)

850mb temps (temperature in Celsius around 4,000′) look like this right now over Salem from the morning/midday runs:

MODELSUNMONTUEWED
GFS ENSEMBLE AVG+17+20+20+20
ECMWF ENSEMBLE AVG+20+22+23+24
GEM ENSEMBLE AVG+20+22+23+23

I based my forecast off +22 to +23 degree temps.

(kptv)

This tells me we’re not going to see a major/historic heatwave, but a more typical mid-summer event. 591dm heights oriented like this don’t produce a hot/gusty easterly wind across the Cascades and no models are showing that hot downsloping. Instead we’ll just experience a shutdown of the cooling onshore breezes for 2-3 days with the hot atmosphere overhead. That should push us up to right around 100 degrees Monday-Wednesday. Sometimes this setup (no dry east wind) can lead to relatively high humidity as small amounts of marine air seep into the I-5 corridor...we’ll see.

The heat next week will also ensure that July ends up as a warmer than normal month.

Enjoy the cooldown the next few days!