It’s been a summer marred by record-shattering, deadly heat in the Pacific Northwest and yet another significant heat wave is on the way. Triple-digit temperatures will roast cities like Portland, Ore., Medford and Spokane, while the risk of wildfires ramps up over the region.

The forecast coincides with the release of the Intergovernmental Panel on Climate Change’s latest assessment review of climate science, which notes a firm link between human-caused global warming and top-tier heat events, like the late June episode that brought a high of 108 degrees to Seattle and 116 degrees in Portland.

This event will not be as intense as the late June heat wave, but Seattle, Tacoma, Portland and Eugene, Ore., are all under excessive heat watches with temperatures peaking between Wednesday and Friday before relenting some over the weekend.

The area around Medford, Ore., has been upgraded to an excessive heat warning for “dangerously hot conditions” set to begin Tuesday and not ease until Saturday. By Wednesday, Medford could approach 107 or 108 degrees.

At least 25 million Americans are slated to experience highs eclipsing 100 degrees over the upcoming week, including many in California’s Central Valley, the Willamette Valley in Oregon and the Washington state interior east of the Cascades.

On Monday, the ingredients for the upcoming sizzler were beginning to come together. Surface high pressure banked well offshore over the northeast Pacific will bring northerly winds over the water paralleling the coast, keeping the breeze over land light and variable. At the same time, a “heat dome” at the mid-levels of the lower atmosphere will build in from the northwest, inducing a northwesterly continental flow from British Columbia.