An extreme and long-lasting heat dome is forecast to hit Oregon late this week, spiking temperatures as high as 110 degrees and potentially lasting a week or more.

The blistering temperatures could impact Oregon’s electrical grid, increase wildfire danger and make urban centers deadly for the elderly and those without air conditioning, officials said.

The heat is forecast to begin Thursday night — the Fourth of July — and peak Friday and Saturday. In the Willamette Valley, there’s a 15-20% chance of temperatures reaching 110 degrees Saturday and a good chance of three days above 100 degrees.

In Medford, there’s a 30-40% chance of temperatures reaching 115 degrees and five days forecast above 100 degrees.

“I think this is an event that will be remembered,” National Weather Service meteorologist Shawn Weagle said. “This has the potential to be a high impact event.”

The heat isn’t expected to reach the levels of the 2021 heat dome that shattered state records with temperatures of 117 to 118. However, this event is expected to last longer, with a second heat wave possible next week.

“There just isn’t much of a break,” Weagle said.

Deadly heat across Western Oregon

The most concerning time period is Friday, Saturday and Sunday, when temperatures are forecast to reach 98 to 105 across wide swaths of the Willamette Valley. Nighttime temperatures may only drop as low as the 70s.

The farther south you go, the hotter it gets. Medford’s forecast is a blistering string of high temperatures — 104 on Thursday, 110 on Friday, 111 on Saturday, 108 on Sunday and 104 on Monday.

“We’re most concerned about people without access to air conditioning and in apartments,” Weagle said. “The fatalities we saw in 2021 were people without access to cooling.”

In the 2021 heat dome, 123 people died in Oregon because of the heat wave, according to the Center for Health Statistics.

How long will the heat wave in Oregon last?

The first heat wave lasts from Thursday night to Sunday evening, Weagle said, before it breaks somewhat by Monday and Tuesday.

Problem is, “the climate prediction center is putting a moderate risk that the heat lasts into a second week,” he said. “If that happens, we could see a brief cool down before it heats back up for a prolonged period.”

The concern is two weeks of temperatures above 90 with multiple hits above 100 degrees, Weagle said.

“The longer these (heat waves) last the harder they are on people,” he said.

Escape from the heat on the Oregon Coast

The best place to escape the heat, as ever, will be the Oregon Coast, where temperatures are forecast to stay in the 70s, with Tillamook and Astoria reaching the 80s.

“They’re still forecast to get that onshore flow from the ocean, which will cool things down” Weagle said.

Wildfire danger likely to increase in Oregon

Wildfire season has stayed quiet in western Oregon so far this season, with cooler and somewhat wetter conditions than normal. Central Oregon has been more active.

However, a long-stretch of such hot and dry weather could dry out fuels rapidly and increase wildfire danger quickly, leading to a longer summer stretch at high wildfire risk.

What is a heat dome?

As for what’s forecast to cause the heat dome, it’s “a very strong ridge of high pressure that pushes the air down and heats it up,” Weagle said. “Combined with the strong sunshine this time of year and the hot air mass from the southwest, all those factors come together in this heat dome.”

Zach Urness has been an outdoors reporter in Oregon for 16 years and is host of the Explore Oregon Podcast. Urness is the author of “Best Hikes with Kids: Oregon” and “Hiking Southern Oregon.” He can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on X at @ZachsORoutdoors.