Oregon’s first extreme heat wave of the summer may break records, according to a state climate official. Some areas of the state will reach more than 100 degrees starting Thursday, and the heat is expected to increase through at least Saturday.

The abnormally high temperatures, part of a multiyear warming trend in Oregon, are prompting concerns about health in a state where many homes lack air conditioning. The extreme heat could also set the stage for a more active wildfire season in the months ahead.

Related: Oregon cities prepare for a very hot Fourth of July weekend

Large parts of Oregon, including the Portland metro area, Medford and Central Oregon, will be under an excessive heat watch ahead of the long Fourth of July weekend, according to the National Weather Service.

Medford is forecast to reach above 110 degrees on Friday and Saturday, potentially creating a historic event for this time of year, according to Oregon state climatologist Larry O’Neill. The Portland metro area is forecast to reach the low 100s starting Friday.

“It may seem like 100-degree weather is normal during the summer, but it’s actually fairly abnormal,” he said.

For the past four years, Oregon summers have trended hotter and extreme heat waves, like the one starting Thursday, are happening more frequently and increasing in intensity.

Since the late 1930s, places like Eugene and Portland have reached triple-digit temperatures about 100 days total, O’Neill said, which equates to an average of about once per year.

That milestone is happening more frequently in the last four years due to climate change, he said.

“Since 2020, for instance, Eugene has had 14 days above 100 degrees and Portland has had 16 days above 100 degrees,” he said. “So, a fair amount of the historical days above 100 degrees have happened just in the last few years.”

Oregon summers have warmed by around 3 degrees Fahrenheit, O’Neill said. And most people in the Pacific Northwest are not yet prepared for high temperatures. Heat waves that reach more than 100 degrees for several days in a row can make heat-related illnesses like heat exhaustion or heat stroke more impactful, he said.

An Oregon Department of Energy study found that many of the state’s most vulnerable people lack sufficient cooling equipment in their homes. They include people living in manufactured dwellings, mobile homes, recreational vehicles, publicly-supported housing and employer-provided agricultural workforce housing.

In 2021, an extreme heat dome left nearly 100 people dead from heat related illnesses in Oregon, most in Multnomah County, with many found alone without air conditioning.

Since then, the state and cities like Portland have launched incentive programs that help residents pay to install heat pumps in their homes.

The state also created a program that aims to install 500,000 heat pumps across Oregon by 2030. The Oregon Heath Authority said Monday that it’s delivered 412 air conditioners to eligible Oregon Health Plan members so far this year. The agency has also distributed other devices, like air filtration systems and portable power supplies, to help people adapt to climate change.

Potential for an active wildfire season

The intense heat and warmer-than-normal weather could also bring some worry for an active wildfire season, O’Neill said.

“What happens in these earlier season heat waves is that it really drives very high rates of evaporation. and so it basically dries out the soils really quickly,” he said. “Any benefit we got from the spring precipitation will be gone, and what this will do is it’ll kind of set the stage for a much drier than normal conditions for the rest of the summer, because we’re not going to expect any more rain at this point or very little.”