You could check weather.com to get an approximation of what the wind speed is supposed to be.
Or, you could buy an anemometer and mount it 33ft in the air, as recommended. http://www.weathershack.com/education/anemometer.html
That still won't tell you what the actual windspeed was/is on your ride.
You could buy a handheld anemometer and stop at intervals during your ride to check the windspeed.
http://www.inspeed.com/anemometers/default.asp