Many mechanisms and factors are responsible for winds in mountainous areas. A mathematical model was developed on the premise that mountain winds are the result of vector addition of wind components generated and modified by these influences. The functions and techniques used in the model were formulated to define and integrate such components of the resultant wind in mountainous areas as valley-mountain wind, slope wind, sea breeze and land breeze, larger scale wind systems, and sheltering and diverting effect of topography. The model is designed primarily for use in estimating wildland fire danger and computing fire spread in southern California. Data were obtained mainly from the San Bernardino Mountains of southern California. Model winds were computed and compared with available observed winds at four research sites in the San Bernardino Mountains. The model output compared well with observed wind velocities. Published by American Meteorological Society. Abstract reproduced by permission.