Forecast Tip:
If there is sufficient moisture in the air and a forcing mechanism like a cold front (for example) is approaching the area, then there is an increased probability that precipitation will occur.

Clouds and precipitation are formed by the upward motion of air. Therefore, there must be a mechanism present to lift the air. Fronts often serve as such a mechanism. Air on one side of the front typically blows in a different direction from the wind on the other side, causing the air to converge, or pile up right along the frontal surface.

Since this air has to go somewhere, it rises. As air rises, the moisture in the rising air cools, condenses and forms clouds and precipitation.