Local winds are caused by differences in air pressure due to uneven heating of land and water surfaces. During the day, sea breezes and valley breezes blow in from cooler waters or valleys to replace rising warm air above heated land or mountain surfaces. At night, land and mountains cool faster than water or valleys, so mountain breezes and katabatic winds blow down from elevated areas. Foehn and chinook winds are gusty winds caused by warm, dry air descending on the leeward side of mountains after being cooled and dried on the windward side.