Winds blowing down mountains often bring unusual warmth. As air descends it is compressed, which warms it. In addition to being warmed, the air's relative humidity decreases as it flows down mountains. This helps clear out clouds or fog, allowing sunny skies to add to the warmth.

As air rises it expands and cools. If air cools enough, the humidity in it begins condensing into fog, clouds, rain, or snow. Rising air cools at the rate of about 5.5 degrees for each 1000 feet it rises. Upslope winds sometimes bring widespread fog to the plains and rain and snow to the hills and mountains.

At right the land cools down more quickly than the ocean. Cold air sinks over the land and pushes out to the ocean the air over the ocean is still warm, so it rises. The colder air moves into replace it, causing a land breeze.

Land and ocean breezes happen only in hot sunny weather. They are convention currents caused by the land and the ocean heating up and cooling down at different rates. During the day the land heats up more quickly than the ocean. Warm air rises from the land and forms an area of low pressure. Air moves in from the ocean to replace this rising air, causing an ocean breeze.

A wind is described by the direction from which it is coming. For example, a west wind comes from the west, a north wind comes from the north.