Summarized wind data within the County are extremely limited. Records covering a 33-month period at the Santa Rosa Army Air Force base show the predominating wind direction to be from the south and southeast. Only 1/2 of 1% of the time were winds of 25 mph or higher reported, and winds in excess of 12 mph were observed 10.5% of the time. Winds were less than 4 mph 37.8% of the time.
Wind direction is profoundly influenced by local topography. In general it may be assumed that winds tend to blow inland from the ocean during summer afternoons in areas that are not protected from such incursions of marine air. Under similar conditions marine air may also flow northward from the San Pablo Bay Area over the southern part of the County. Winter storms bring strong southerly winds over most of the area.
It is estimated that wind speeds may reach 40 mph over most of the area as often as once in 2 years, increasing to 80 or 85 mph as often as once in 50 years.