Anabatic wind

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Anabatic wind, or upslope wind, is a warm wind that blows up a slope on sunny days. It starts when the sun heats a hill or mountain top, warming the air above it. The warmer air becomes lighter and rises, pulling air from lower areas up the slope. As the air rises, it can cool and form clouds, sometimes bringing rain or thunderstorms. Anabatic winds help soaring gliders gain height, but they can slow cyclists on downhill runs. They usually occur during daytime in calm, sunny weather. A related wind is katabatic wind, which blows downhill at night when the ground cools the air near the surface faster than the air over the plains.