A Warm July Ends With A Heatwave

July 26, 2021

9:00pm Monday…

It’s vacation season in the Pacific Northwest; the best weather of the year! So I’ll be joining many of you travelling across the region the next week and a half. Heading out for camping in parts of southern Oregon. No posts during that time, unless something really serious pops up (major fire close to us, huge earthquake, volcanic eruption, tsunami, etc…). I’ll be back at work Sunday August 8th.

The end of July is quickly approaching and it’s been a warm month! No record-breaking heat, or heatwaves, but consistently warmer than normal. It appears we’ll end up with at least the 5th warmest July on record, likely #3 or #4.

The western 1/3 of the USA has been sizzling so far this month, following the warmest June on record for some.

We’ve been “lucky” west of the Cascades, picking up just enough cooling onshore flow to keep us near/below 90 degrees most of the month. Portland has seen (12) 90 degree days so far this year

Yet, just slightly farther removed from that ocean air, both Salem and Eugene have seen over 20 days at/above 90!

Looking ahead, we have a heat wave on the way Wednesday-Saturday. This is what we’re thinking this evening for Portland:

No record highs, since they are generally 100+ this time of year. But four 90+ days to wrap up July.

Why is it turning hot again?

Strong high pressure bringing heat over the Rockies is far enough east to keep our temps reasonable again tomorrow. That “594” contour centered over Colorado is the center of the upper-high.

But you see it snuggles up a bit closer to us Friday and Saturday. Here’s midday Saturday; the ridge of high pressure has amplified, and southerly flow is in charge across the West Coast. This MAY bring thunderstorms north into the Cascades and Eastern Oregon. There are even a few GFS and ECMWF ensemble members sending a disturbance north with showers/thunderstorms WEST of the Cascades this weekend. But not enough to put it in the forecast. Just be aware that this weekend is not “guaranteed” dry. Keep an eye on the forecast.

This pattern doesn’t produce a hot easterly wind over the Portland area (ridge is too far east), which should keep us below 100 degrees…but just barely! Then Sunday and beyond the ridge weakens; we’re back to reasonably warm temperatures for the first few days of August. This is Tuesday (August 3rd)

By the way, we are at day #41 without rain in Portland. The last MEASURABLE rain was June 15th. There WAS a trace at PDX on July 1st. Assuming we don’t get rain in the next 12 days (possible), we’ll be up in the “top 5” range for dry spells. But for now we’re a long way from that 71 dry day record

A few more notes:

  1. I don’t expect high humidity during the upcoming heat wave, UNLESS we get some showers or thundershowers Saturday/Sunday.
  2. Overnight temperatures will be turning very warm, mid-upper 60s. This isn’t as extreme as the historic heatwave back in June, but it’s still worth checking in on elderly friends/relatives.
  3. Southerly flow = overhead fire smoke from California fires. Expect increasing haze and yellow/orange sun after Wednesday. Low-level smoke is UNLIKELY west of the Cascades since wind will be coming from the northwest and west.

Stay safe during summer vacation travels!

Chief Meteorologist Mark Nelsen