Portland’s weather will remain nice for much of next week, and western Oregon could be on pace for the longest stretch of temperatures above 100 degrees on record — a situation that meteorologists say could have repercussions throughout the summer and bodes ill for wildfire season.
The latest forecast from the National Weather Service is alarming: “Extremely dangerous… intense, widespread and prolonged… increased risk of heat-related illness.”
Hydrate yourself. Hydrate yourself. Hydrate yourself.
So is it a heat wave? A heat dome? Both? And what is an omega blocking pattern?
Meteorologists say we are definitely in the middle of a heat wave, which can have multiple causes and simply refers to a prolonged period of above-average temperatures.
With a high pressure system parked over much of the West Coast, temperatures in Portland are expected to rise from a forecast high of just under 100 degrees Friday to 104 degrees Tuesday, according to the National Weather Service. Portland’s average daily high for July is 82 degrees.
The night will not bring much respite, with temperatures expected to range between 15 and 21 degrees, compared to average minimums of 14 degrees.
“The temperatures are stacking on top of each other,” said David Bishop, a meteorologist at the agency’s Portland office. “When it’s not getting cooler at night, it’s a lot easier to get temperatures up to 105 degrees Fahrenheit.”
Models show some cooling midweek, but not by much.
“Temperatures aren’t going to drop much,” said Larry O’Neill, a state climatologist and assistant professor at Oregon State University. “They’ll stay around 35 degrees for the next 10 to 20 days.”
So, is it a heating dome? Opinions vary.
Cliff Mass, a professor of atmospheric sciences at the University of Washington, says it’s a relatively new term, popularized by the media, that doesn’t quite describe what’s happening. “Everybody uses it, but it doesn’t really make sense.”
Kelley Bayern, a meteorologist for KOIN 6 News, said not all heat waves are heat domes and she wouldn’t want to overuse the term.
But “it’s potentially deadly heat and I want to get people’s attention,” she said.
O’Neill says it’s a legitimate term that he also uses and that is appropriate in the current context.
Regardless, all three agree on what this pattern means: a massive high-pressure system in the upper atmosphere — at about 18,000 feet — with descending air that compresses and warms as it descends, supercharging surface temperature readings.
They also agree that this pattern has given rise to what is known as an “omega blocking pattern,” an unusually stable ridge of high pressure wedged between two lows to the east and west, resembling the capital Greek letter omega (Ω) on a weather map. This forces the jet stream northward and impedes normal ocean flows that might otherwise push the high pressure system inland.
“This one is so stagnant that it doesn’t move anywhere for days,” Bayern said.
Tropical Storm Beryl, which is expected to regain hurricane strength as it moves closer to the Texas-Mexico border this weekend, could also be a factor in how quickly the high pressure ridge moves and the weather cools here, O’Neill said.
“It’s a wild card that could block the movement of the high pressure system,” he said.
Another worrisome aspect of a prolonged heat wave so early in the summer is that evaporative effects could exacerbate wildfire risks throughout the summer as Oregon enters its dry season.
Just two weeks ago, the Oregon Department of Forestry released its three-month outlook. It said Oregon was officially out of drought and predicted relatively warm weather from July through September, “but no extreme/prolonged heat.”
“That’s all over now,” O’Neill said. “The heat and the low humidity are causing a massive evaporation of moisture from the soil. The fuel moisture is going to be very low. Everything is hardening and drying out, so it’s going to be a very interesting fire season.”
He added that dry soils make heat worse in general, thus worsening the effects of global warming.
“This July is shaping up to be the hottest we’ve ever had,” he said. “It’s something we’re going to be monitoring very closely.”
– Ted Sickinger is a reporter with the investigative team. You can reach him at 503-221-8505, tsickinger@oregonian.com or @tedsickinger
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