prevailing wind direction

(Or prevailing wind.) The wind direction most frequently observed during a given period.

The periods most frequently used are the observational day, month, season, and year. Methods for determination vary from a simple count of periodic observations to the computation of a wind rose.
Compare resultant wind.

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.