Why does the wind blow? The uneven heating of the earth's surfaces causes wind to blow, because different surfaces heat and cool at different rates. Hot air rises and cold air sinks. Air must flow i to take the place of the rising warm, or sinking cold air. Wind is created!

Unstable vs. Stable air:

Unstable air masses form when two air masses of different temperature and humidity conditions collide. Where this happens is known as a weather front. Stormy weather usually takes place. Stable air has the same temperature and humidity conditions throughout.

Weather Fronts: Weather fronts occur when air masses of different temperature, humidity and pressure conditions meet.

Cold Fronts occur when the leading edge of a cold air masses meets a warm air mass ahead of it. Unstable weather will occur at the front (boundary).

Warm Fronts occur when the leading edge of a moving mass of warm air, meets a cold air mass ahead of it.