Wind 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. 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. There is a steep humidity gradient during the summer between the marine air and the drier and warmer air of the inland locations. Most of the winter cloudiness is associated with migrating storms that move inland from the Pacific. The cloud patterns of these storms are essentially the same over all parts of the County. In the summer, however, the cloud patterns are more localized.