Onshore and Offshore Winds and Weather

Q: How do an onshore and offshore wind affect our weather?

A: A land breeze (offshore) affects our weather opposite of a sea breeze (onshore). A land breeze keeps the ocean-cooled air and cooling fog over the ocean. Also, as air descends our mountains into the Bay it compresses and heats. Our record warm high temperatures occur during a land breeze event.

As for pollution, a sea breeze brings in cleaner air from the Pacific Ocean and transports our pollution to the east and southeast through the Carquinez Strait and Santa Clara Valley. A land breeze (offshore) stops this venting. After a few days, pollution levels increase and usually a "Spare the Air" day is declared.