An anabatic wind is an upslope wind driven by solar heating of a mountain surface. As the sun warms the slope during the day, the air immediately above it heats by conduction and convection, becoming buoyant relative to the free atmosphere at the same altitude. This warmer, lighter air rises along the slope, creating an uphill breeze that typically begins mid-morning and strengthens through the afternoon.
Anabatic winds are the daytime counterpart of katabatic (downslope) winds, which flow downhill at night as the surface cools. Together, they form the mountain–valley breeze cycle: anabatic winds carry air up the slopes by day, feeding a return flow at altitude towards the valley centre; at night, katabatic winds drain cold air down the slopes into the valley floor. This diurnal cycle is one of the most regular local wind patterns on Earth.
For meteorology and outdoor activities, anabatic winds have several important effects. They transport moisture upslope, often triggering afternoon cumulus cloud formation over mountain peaks and ridges — visible as the daily buildup of fair-weather clouds that dissipate by evening. Paraglider and hang glider pilots exploit anabatic lift along sun-facing slopes. In fire weather, anabatic winds are dangerous: they push flames rapidly uphill, where fire already tends to spread faster due to pre-heating of fuel above. The strength of anabatic flow depends on slope angle, sun exposure, surface type (rocky slopes heat faster than forested ones), and the ambient atmospheric stability.