Bay Area air: clear this week, but haze, smoke could return by Friday

Hazy skies are out, clear skies are in — that’s the message from meteorologists this week as the Bay Area enters a brief respite from wildfire smoke.

Good to moderate air quality prevailed for much of the region Monday, a trend that is expected to continue through the week, said a spokeswoman for the Bay Area Air Quality Management District.

But meteorologists warn that the upcoming weekend could bring a return of unhealthy air and smoke as south-blowing winds gather strength over Oregon and Northern California.

By Friday, the marine layer cooling the Bay Area will all but disappear, ushering in another round of oppressive heat similar to the conditions that sent thermometers skyrocketing over Labor Day weekend, said Brayden Murdock, a meteorologist for the National Weather Service.

The expected heat spell could create hazards for firefighters, sapping vegetation of any remaining moisture and further drying out underbrush. Meteorologists are watching for persistent winds and low humidity, red-flag conditions that could spell danger for fire crews.

Places like Livermore, Gilroy and King City will be the hardest hit by the heat and could see triple digit temperatures, Murdock said. The rest of the region is also expected to see dry heat and smoke that may make weekend activities unpleasant.

The change in wind patterns could carry smoke down from the Oregon wildfires or the record-breaking August Complex fires raging across nearly 847,000 acres of Mendocino and Humboldt counties.

Strong winds are a “double-edged sword” when it comes to air quality in the Bay Area, Murdock said. The same winds that usher in smoke also prevent smoke-filled air from becoming stagnant.

“It’s a conveyor belt, but at least it’s moving,” he said, referring to the wind patterns expected this weekend.

Experts said it is difficult to predict air quality, something kite surfer John von Tesmar knows well.

Von Tesmar owns Kite the Bay and he’s out on the water teaching people to kite surf five days a week. This has been his busiest summer in 11 years, but the recent unpredictable winds and smoky conditions have led to more than a few canceled lessons, he said.

It’s much harder to get a kite in the sky with an onslaught of smoke girding the bay, von Tesmar said.

“The north winds might bring smoke this weekend, but I’m hoping it’s not as thick as it was,” he said.

Nora Mishanec is a San Francisco Chronicle staff writer. Email: nora.mishanec@sfchronicle.com. Twitter: @NMishanec