The rain that began Wednesday morning is expected to continue periodically through Friday evening in the San Francisco Bay Area, and is it bringing some much-needed improvements to the air quality in the region, officials from the National Weather Service said Wednesday morning.

“Air quality will keep improving as the wind flow increases and pushes it through the area,” said Steve Anderson, a weather forecaster with the National Weather Service. “The wind is the main transport – the rain has little to do with improving air quality. It’s which way the wind blows.”

After a week in which air quality alerts reached “purple,” or “very unhealthy,” levels, air quality was listed Wednesday afternoon as “Good,” with an air quality index of 22.
The weather system is also expected to bring snow to parts of I-80 and U.S Route 50 over the Sierra Nevada mountain range.

“If you’re travelling to grandma’s house in Reno over the Sierra Nevadas, you’ll need chains tonight,” Anderson said.

The rain is expected to subside through the weekend before another burst of heavier rain moves through in the middle of next week.