Break out the flannel swimwear? The 90s are coming back

Break out the flannel swimwear? The 90s are coming back

SEATTLE -- Paging Eddie Vedder and Chris Cornell, the 90s are coming back to Seattle... or at least as far as thermometers are concerned. And just like the Grunge movement, there's probably a good dose of people who love it and others who wish it would just go away.

(And I'm sure there are some around to who the 90s have never ended...)

Our second heat wave of the year is building into the Pacific Northwest, promising to bake much of the region in 90-plus degree heat for at least two days, and likely three days, and possibly more.

High pressure is becoming entrenched over the region, helping to keep away the clouds and warm up the atmosphere a bit. In addition, a strong thermal trough (also known as a "heat low") is expected to build just off the coast on Friday and park there all weekend long.

Normally, low pressure brings visions of clouds and storms, but in this case, it's quite the opposite. The low is formed in the area of maximum heating where you have so much hot air rising that it leaves less air near the ground, and thus lower pressure.

To make matters hotter around here, that trough will draw in air from the surrounding area to replace the air that is missing. In our case, when the trough is to our west, it generates an easterly wind, which presents a double whammy of heat. First, that air is originating from Eastern Washington where, if you've ever been over there in August, you know it's usually pretty hot to begin with. Second, as that air goes up, then sinks down the western foothills of the Cascades and Olympics, it gets even hotter due to a physical process called compressional heating.

(It also dries out the air, making this more of a comfortable desert-like heat than an oppressively muggy East Coast heat. I suspect relative humidity readings will be around 20 percent during the day.)

Put all that together, and it's time to start scooping out the ice cream and scoping out the places to stay cool.

Highs on Friday are expected to reach the mid 80s around Seattle, and low 90 along the foothills and southwestern Washington as the thermal trough and east wind begin to build. (Places near the water get a short reprieve as the winds turn to the north on their way to veering east, thus bringing a seabreeze off the water and highs in spots like Edmonds, shorelines of Seattle, Des Moines, etc will be in the upper 70s).

Thinking you'll just jaunt over to the coast to escape the heat? Think again. With moderately strong east wind in place, it'll push back the cool ocean air from coming inland, and instead blast the coast with the heat from the interior locations, plus some spots like Forks and others just west of the Olympics also get that same mountain-heating effect. (Yes, many times Forks ends up hotter than Seattle in these situations.) So upper 80s on the coast too.

We spend each day Saturday, Sunday and Monday stuck in this east wind as the thermal trough just meanders out there. Another "feature" of the east wind is it tempers nighttime cooling, so lows will only drop into the mid-upper 60s each night. But as each night gets a little warmer, each day in turn gets a little warmer as we have a warmer temperature to start with when the sun comes up the next morning. Thus, highs on Saturday will likely cross into the low 90s in the Seattle area, and mid-upper 90s east and south (a touch cooler north). By Sunday, probably a degree or two warmer than whatever we reach on Saturday.

By Monday, we slowly start the seeds of change as the thermal trough is finally expected to drift inland and perhaps move east of the coastline. That will switch the winds along the coast to a westerly direction (remember, the winds are trying to fill in the low, so they chase after it) and bring temperatures down into the 70s there. But on the other hand, the day the thermal trough is over the Puget Sound region is typically the hottest day so we are adding a little more to the expected high temperatures -- still in the low-mid 90s, and maybe some spots near the foothills maybe up near 98 degrees. (Oh great, now we have to page the Lachey brothers too?)

Beyond Monday, the forecast is a question mark. Computer models try to leave the heat low around our area still on Tuesday, and only slowly move it to our east on Wednesday, not really showing any significant cooling until Thursday. But that's not how Seattle heat waves usually roll -- about 3 days is it, maybe 4.

There is some precedent for a minor cool down -- sometimes we lose the east wind, but don't get the west wind yet, and that has the effect akin to when you turn the stove burner off, it still stays warm for a period afterward. Thus Tuesday could end up cooler, but still very warm, like mid-upper 80s, and that's what we are going with for now.

I get the sense that we'll probably cool off even more on Wednesday and definitely by Thursday, but we'll have a better look once we get into the weekend.

In the meantime, I'm going to start researching if they make flannel sunhats...

What records are we aiming for?

Friday's record high of 92 appears safe. Saturday's record high of 90 and Sunday's record high of 92 are both in jeopardy. Monday's record high is 98, which should be safe, but I'll give at least some small odds we could get there if, say, we get into the mid 90s on Sunday.

'Juneuary, Who?' We're hotter than L.A. even before this next heat wave!

For all the gnashing of teeth for our cool June and summer so far, we have actually been significantly warmer than parts of Los Angeles and San Diego. So far since June 1st, the average high in Seattle has been 70.7 degrees, versus 68.7 degrees for both Los Angeles (LAX) and San Diego (Lindbergh Field.) But that is more a factor of just how persistent the fog has been in Southern California -- I just checked and November was warmer in L.A. than July.

How often does it get hot around here?

Well, so much for statistics. In data up through 1997, Seattle averages about 25 days a year at 80 degrees or warmer, 10 days at 85+, and 2-3 days at 90+ and a 95+ day every-other year. But I gather if we factor in recent data, that might change, especially because since last July, the temperature has hit 90 or better 10 times and crossed 95 four times. So we are well over our quota but apparently Mother Nature has not received the memo.

We are also in the realm of matching last year's super hot summer for number of days at or above 90 degrees at seven. (Record is 9 set in 1958.) Seattle has already had three days at 90 or hotter, with three more -- maybe four -- in the realm of possible.

Stay cool out there!