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

Warm & Dry July Continues, Plus Some Good Fire News

July 21, 2021

8pm Wednesday…

We’ve been in a surprisingly stable weather pattern ever since the heat wave ended in late June. Warmer than normal, but not much heat. We are three weeks into July; every day has ended up between 75 and 90 in Portland. Today was especially nice with partly cloudy conditions all day long. We’ve seen lots of days in the mid-upper 80s in Portland, but only hit 90 once (on the 6th). That’s due to a persistent weak onshore flow; that cooler ocean air pouring inland each evening. It tends to come up the Columbia River to Longview and then the metro area. That’s different than the “southwest push” coming in over the Coast Range we saw right at the end of the heat wave.

Salem and Eugene, farther removed from those cool northwest breezes, have each seen 9 and 10 days above 90. That’s quite a difference! Although none of those days made it above 92 in Salem. Right now Salem is seeing it’s 4th warmest July on record; due to consistently warm temperatures vs. a series of hot spells.

A very consistent upper-level pattern remains in place the rest of the month (if models are correct). Right now a hot ridge of high pressure is right over the Rockies. At the same time a weak trough is moving by to our north; thus the cooler weather the past two days, even up in the mountains.

By this weekend, the last full weekend of July, the high edges a bit closer. So we turn a bit warmer as onshore flow backs off again. We might even hit 90 in Portland…maybe.

Then the ridge moves farther away, back into the Great Plains early next week. 9 days from now, Friday the 30th shows us in the “Goldilocks Zone” west of the Cascades. Warm, but no heatwave and not much “hot” weather.

All models agree with this general setup the next 7-10 days.

What This Means

  1. Temperatures remain above normal, but a heat wave is unlikely through the end of July west of the Cascades
  2. Most fire smoke will continue to remain over/east of the Cascades. That southwest flow carries most of it well east of us. I don’t expect any sort of “smoke episode” in the Portland area the next 7-10 days
  3. A widespread outbreak of thunderstorms is very unlikely in this pattern, even east of the Cascades
  4. No chance for rain, guaranteed dry weather continues next 7-10 days

Speaking of rain, we’ve only seen a TRACE so far in Portland this month. It was a few spots of drizzle out of the marine layer on the 1st. A trace means it can’t be measured…less than 0.01″. July is our driest month of the year in Portland; we only average 0.50″! August is close behind at 0.54″. We almost never have a truly “wet” July. But I remember both 1983 and 1993 were showery and cool; quite rare indeed. Those were “green tomato” summers…


Fire season is off and running big-time this year. Numerous large (greater than 100 acre) fires have burned in both Oregon and Washington. This has been fueled by 3 years of drought in southern Oregon plus the driest spring on record for many areas. Then an unprecedented extreme heat wave baked the region in late June; a perfect setup for a bad fire season. At this moment there are 5 large fires burning in Oregon

There is one fire grabbing all the attention right now, the Bootleg Fire burning through the Fremont National Forest. That’s between Bly, Summer Lake, & Paisley

The Jack and Elbow Creek fires are large as well, but notice they aren’t growing quickly. Good news there. The Bootleg Fire is about to become Oregon’s 5th largest on record, passing up the Buzzard Complex

And I had better mention the “Tillamook Burn” because each time I show this graphic, someone accuses me of forgetting that one. Actually there were THREE large Tillamook Burns (and one smaller), beginning in 1933; it was called the “six year curse”. All in the north Coast Range between Banks and Tillamook.

The bad news, of course, is that we don’t have any cool/rainy weather systems headed into the region. We wouldn’t expect that in July anyway. Extremely dry fuels will remain that way until further notice.

The good news?

  1. We don’t see a real heatwave coming for the region over the next week or so.
  2. Lightning activity has been minimal to almost non-existent so far this season and will remain that way through the foreseeable future.

Considering the current very dry fuel conditions, IF we get a widespread outbreak of dry thunderstorms, then fire season could explode. Let’s hope that doesn’t happen. Typically that setup would involve a southerly or southeast flow in the upper-atmosphere. For now I’m not seeing that over the next 7-10 days.

That’s it for now; enjoy the near-perfect summertime weather west of the Cascades. Yes, a bit on the warm side, but no heatwave!

Chief Meteorologist Mark Nelsen

Cooler Late Week, Then Warmer; Dry Summer Pattern Here To Stay

July 12, 2021

9pm Tuesday…

In the past week we’ve seen warmer than normal temperatures persist west of the Cascades, although no real hot days in the metro area. Lots of 80s, before & after the marine push last Wednesday/Thursday. Yet just one day at 90 degrees.

Meanwhile Salem has seen 8 days at/above 90 so far this month. Why? We are in a classic “northwesterly flow” regime. The setup has been very stable for over a week. Wind is coming in off the Pacific each afternoon/evening to replace hot air rising over the interior of the Pacific Northwest. The Columbia River gap allows lots of that cooler marine air to come up through Longview, Kalama, Clark County, and into the Portland metro area. This morning’s satellite image (8am) shows enough cool air and moisture for low clouds in a good chunk of this area. Clouds tend to form central & eastern metro first because the marine air is bottled up against the the western Gorge. This is why west metro tends to be sunnier more often summer mornings than the east side.

Farther south, in the Willamette Valley, no morning clouds = warmer. The layer of cool air is thinner there. Look at the effect on high temperatures today. 77 at Longview to 90 at Salem.

Strong westerly wind through the Gorge keeps Hood River comfortable, but by the time you get to The Dalles the airmass has warmed. Way out in Hermiston, today is the 25th day at/above 90 degrees. They haven’t seen a cooler than average day since June 16th!

There are 4-5 significant fires burning across Oregon this evening. This is an amazing visible satellite image considering it’s only July 12th. You can see a new fire south of Detroit Lake (Bruler), Grandview fire NE of Sisters, Jack fire NW of Diamond Lake, and the massive Bootleg fire north of Bly

That Bootleg fire exploded in size Saturday, becoming a “mega-fire”. That’s a fire over 100,000 acres in size. It didn’t change much through this morning, then you can see it has exploded again this evening. I estimate a 25-30 mile long “fire-front” based on GOES-17 fire detection

Oregon has seen 22 megafires since 1980, most of them in the eastern half of the state. Of course 5 of those just occurred over/on the slopes of the Cascades last September. You can find a recap of that event here: https://fox12weather.wordpress.com/historic-september-2020-fires-labor-day-windstorm/

What’s Ahead?

  1. Dry weather continues across the region through at least the next 10-15 days.
  2. A cooldown arrives Wednesday and spreads east of the Cascades Thursday-Saturday
  3. Then we warm up again early next week
  4. There’s no sign of a heat wave west of the Cascades through at least the 20th

Check out the 500mb anomaly map (from the GEM model) for right now. In general we’ve got higher than normal (warm colors) heights overhead

By Friday, a cool trough is sitting just offshore. But notice heights have only come down to around normal for this time of year. The hot ridge has weakened and moved back to the “Four Corners” region. This pattern gives us widespread morning clouds west of the Cascades. High temperatures drop back into the 70s…a refreshing mid-summer weather pattern.

But by Monday the hot ridge is back, just to our east.

It’s still there NEXT Thursday, the 22nd, 10 days from now. This says above normal temps, but not extreme. Especially west of the Cascades.

You can probably guess there’s very little chance for rain in this pattern. No organized weather systems come close to us. Look at a bone-dry ECMWF model forecast the next two weeks: Just a spot of drizzle out of low clouds. Not a single one of 51 ensemble members produces even a tenth of an inch through the 27th!

Let’s hope for very little lightning and no human-caused fires. 3/4 of last year’s fires in the Pacific Northwest were started by people.

Enjoy the rest of the week! Chief Meteorologist Mark Nelsen

Stable & Warm Summer Weather Pattern Continues

July 5, 2021

11pm Monday…

A very brief post to let you know the weather has S-L-O-W-E-D down across the Pacific Northwest. Temperatures in Portland have hit 86 or 87 for the last 4 days! Not a lot of variation there.

We are in our summer dry spell with no significant rain in sight. There could be spots of drizzle west of the Cascades when the marine layer thickens Wednesday morning. Other than that, the ECMWF (GFS looks the same) ensembles show almost no chance of measurable rain the next two weeks. That’s through the 20th. ONE ensemble member out of 50 produces all of 0.10″ rain…

Just as unlikely through at least the middle of next week? A heatwave. No sign of that in the 15 day ensemble average, just the usual ups/downs as marine air surges in and out of valleys west of the Cascades.

That’s it for now.

There’s no need to worry about the lack of rain, there’s nothing you or I can do about it. So enjoy the reliable sunshine while it’s here. I’ll be off the rest of the week.

Chief Meteorologist Mark Nelsen