Seattle weather forecast: What to know about smoke, air quality and heat

Thursday will mark the first day of an areawide cooling trend, following a buildup of heat early in the week.

On Wednesday just after 3 p.m., Seattle reached 90 degrees for the first time this year, the National Weather Service said. The record for the date is 91 degrees, set in 2015.

Winds from the north also brought smoke from wildfires burning in Alberta and British Columbia into the state, in addition to lingering smoke from Fourth of July fireworks. While air quality in some parts of the region had reached unhealthy levels early in the day, by midafternoon it had largely improved to moderate levels.

The National Weather Service said some smoke and haze could persist through Thursday. Across the state, people should make sure they have N95 masks on hand, as well as air purifiers or alternative filtration methods, like a MERV 13 filter taped to a box fan, in preparation for smoke.

While high temperatures on the Fourth of July didn’t set any records in Seattle, it was one of the warmest on record. 

Seattle’s high of 88 degrees on Tuesday was the fourth-warmest July Fourth, behind 89 degrees (1975), 91 degrees (1972) and 92 degrees (2015), the weather service said. 

Temperatures were also high across the globe Tuesday. It was the hottest day on Earth since at least 1979, with the global average temperature reaching 62.92 degrees, according to data from the U.S. National Centers for Environmental Prediction.

Overnight lows in much of Western Washington recovered decently heading into Wednesday, sinking into the 50s. However, SeaTac, Everett and Tacoma reported overnight temperatures in the upper 60s, which provided fertile ground for the heat to build to about 90 degrees Wednesday, the weather service said.

Wednesday was expected to be the hottest day of the week for the interior, while the coast was expected to get some relief from cool marine air Wednesday, dropping temperatures 5 to 7 degrees from Tuesday.

The weather service issued a red flag warning for hot, dry and unstable fire conditions through 7 p.m. Wednesday for the west slopes of the Cascades and southwest portions of the state.

High pressure is expected to break down and onshore flow will blow into the region Thursday, causing temperatures to fall bit by bit each day through Sunday. Thursday in the interior will still be quite warm, though, with highs lingering in the mid- to upper 80s, the weather service said.