Seattle's hottest weekend of the year is coming

The hottest weather of the year so far is forecast to arrive this weekend, with temperatures near 90° expected in Seattle.

Why it matters: With high and low temperatures expected to be well above average this early in July, the National Weather Service says there is an elevated heat risk for vulnerable people and those who live in urban heat islands.

• About half of Seattle lives in heat islands where warmth is trapped by hard surfaces such as parking lots and pavement, making them typically at least 8° warmer than surrounding areas, according to the nonprofit climate research group Climate Central .
• "We will not be getting overnight relief from temperatures falling into the 50s, as Washington is used to, and that's why the heat risk is higher," Harrison Rademacher of the National Weather Service in Seattle told Axios.

Threat level: Not only does intense heat pose health risks , it is also expected to increase the threat of wildfires and exacerbate the state's existing drought conditions .

By the numbers: Seattle is expected to see a high of 81° Thursday and 86° Friday.

• The forecast high is 88° for Saturday and 94° for Sunday. The normal high for July 6 is 76°, Rademacher said.
• Some models are suggesting temperatures close to 94° on Monday as well, Michael Fagin of West Coast Weather told Axios.

How it works: A strong ridge of high pressure — sometimes called a heat dome — is building in the upper atmosphere and moving in from the Pacific, Fagin said.

• Heat domes eliminate cloud cover and cause hot air to sink, making for extremely hot temperatures on the ground.
• Additionally, upper-level wind patterns are pushing the cooler jet stream into Canada and Alaska while sucking in hot air from the south, said Rademacher.

The big picture: The West Coast, particularly California and Oregon, is set to experience a potentially dangerous and persistent heat wave into next week.

• Human-caused climate change is making heat waves more likely, more intense and longer-lasting . It is also making days with extreme wildfire weather conditions more common.

The intrigue: While Seattle is no longer the least air-conditioned city , only about 50% of Puget Sound residents had AC in their homes in 2021, compared to 90% nationally.

• The year this latest data was collected was when a historic heat dome phenomenon brought a 108 -degree day to Seattle.

What's next: The heat is expected to last through at least Tuesday but by Wednesday it should drop down into the lower 80s or high 70s, just slightly above average for the second week of July, said Rademacher.