Refer to figure.
As precipitation falls from a fully developed thunderstorm, it partially evaporates during its descent. This process absorbs latent heat from the air, reducing the air temperature. The cooler, denser air then descends, strengthening the downdrafts within the thunderstorm cell. When these cold downdrafts reach the ground, they spread outward along the surface, creating a gust front at the leading edge of the cold air.