How can I find out the direction of prevailing winds for summer and winter in my area?

The United Stated Department of Agriculture Natural Resources Conservation Service has a tool for determining local patterns of prevailing winds: http://www.wcc.nrcs.usda.gov/climate/windrose.html. ¬†Click on the link for ‘Wind Rose Plots.’ Next, select your state, then select the .gif file for the location and month(s) of the year you are interested in.