Yesterday's high of 106 degrees is about as close as you can get to Portland's all-time record high of 107 degrees, and seriously, could anyone out in that kind of heat tell the difference?

Today's forecast high -- depending on what weather forecaster or agency you talk to -- is somewhere between 105 and 109 degrees.

If you were taking bets, one way to tell where today's high in Portland will top out is to look at where the temperature was yesterday at a particular time.

At 11 a.m. yesterday, the temperature at the airport was 88 degrees. At 11 a.m. today, it was 90 degrees. By 2 p.m., the temperature had soared to 104 degrees, and was closing fast on the record and threatening to create a new all-time high.

Smart money would bet on a high today of 108 degrees, breaking a record that seemed unbreakable, but now seems reasonable.

The last time it was that hot was the week of Aug. 7-10, 1981; on Aug. 8 and 10 it hit 107 degrees. Before that, the temperature reached 107 degrees July 30, 1965.

"I think we're on the fence when it comes to breaking that record, and tying the record of five consecutive 100-degree days," said Dan Keirns, a forecaster for the National Weather Service in Portland.

Keirns said what may put us over the top is an east wind that began blowing near Troutdale this morning, something that had been lacking for the past two days and often makes temperatures rise in the Portland area.

It's also what may the first salvo in the gradual breakdown of the heat wave, namely, an upper level low-pressure system that is meandering off the coast and slowly moving our way.

If it arrives on time (or when the forecast models say it will), the heat wave will gradually begin losing its grip tomorrow, when the high is expected to be at 100 or just below.

"Either way, it's still hot when it's 97, and for the people without air conditioning, it's going to be pretty annoying,'' Keirns said.

The heat low that had been in the Coast Range has moved into the central Willamette Valley, Keirns said, and that's another reason today could be a degree or two hotter than yesterday.

"You had to get almost in the surf yesterday to find relief at the central and north coast,'' Keirns said. "Some of that heat was from all the exhaust from people driving around trying to find a parking space."

Forecasters at Accuweather said the jet stream is unusually far north over western North America, which has allowed this intense heat wave to develop.

Even parts of the Arctic Circle, including the Yukon and Canada's Northwest Territories, aren't escaping the heat, with highs 30 degrees above normal.

Not until it moves off to the east will temperatures begin to moderate, as marine air from the Pacific begins to migrate up the Columbia River and the gaps in the Coast Range.

"If I had wanted weather like this I would have moved to Las Vegas," Keirns said.

At least in Vegas you might have a decent chance of buying an air conditioning unit. In Portland, forget about it.

"We are 100 percent out and so are all our competitors,'' a sales associate at the Delta Park Lowe's home improvement center. Lowe's has sold more than 200 fans in the past few days, and its supply as of Wednesday afternoon was down to one 7-inch fan.

"That would barely blow the papers around on your desk,'' another sales associate said. "We get new deliveries every day, but we don't know what's going to be on them."

Craigslist, however, had numerous postings for air conditioners on sale, anywhere from $75 to $675, some with delivery options.

The forecast high in Las Vegas today is 108 degrees. Yesterday's high was 112.

Other records that could fall today:

If it stays at 90 or above through Saturday, that breaks the all-time record of consecutive days at or above 90 degrees, which was 8 days ending on Aug. 19, 1967.

If it stays at 95 or above through Saturday, that would break the old record of six days, which ended Aug. 11, 1981.

-- Stuart Tomlinson; stuarttomlinson@news.oregonian.com