Smoke from a series of large wildfires burning in Northern California and Oregon is riding steady northerly winds into the Bay Area, lowering air quality to unhealthy levels in much of the region.

The Bay Area Air Quality Management District issued a Spare the Air alert Wednesday that will remain in effect at least through Thursday, but after that, it's unclear if smoky conditions will linger or how intense they might be if they do.

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The district previously issued an air quality advisory through Wednesday but upgraded it to a Spare the Air alert—which bans burning wood, fire logs or other solid fuel—because the air in many places had reached unhealthy levels, particularly in parts of the South Bay and East Bay.

"The forecast models said we'd see impacts from smoke but not as much as we did, so it did catch us a little bit off guard," said Charley Knoderer, a meteorologist manager at the air district.

While the impacts from wildfire smoke are always difficult to forecast, current conditions were particularly challenging to predict because much of the smoke that's drifting into the Bay Area is coming off the ocean, where there are no air quality sensors, and prediction models didn't immediately pick up on the plume's movement into the region.

The smoke is coming in from several massive wildfires, including the Smith River Complex Fire, SRF Lightning Complex and Redwood Lightning Complex fires, the Flat Fire and the Anvil Fire, which along with other blazes, are burning more than 200,000 acres in Southern Oregon and Northern California.

People can monitor the region's air quality by visiting the Air District's interactive map.