The University of Texas at El Paso
riobosque banner


Where air masses meet, there are well-marked boundary zones called fronts. This is where most cloud and precipitation occurs. Buy's Ballots Law tells us that the circulation is anticlockwise around low pressure and clockwise around high pressure. The air flows almost parallel to the isobars but actually 10-15 degrees inwards towards the low pressure.

There are four types of fronts:

Warm front
- when a warm moist air mass rises above a cold air mass, a warm front forms. The gradient of the front is very shallow. Warm fronts occur at the forward edge of a depression (a low-pressure system).

Cold front
- a cold front marks the advance of colder air undercutting warm air. The gradient of the cold front is steeper than that of a warm front, and the rainfall is usually heavier. Thunderstorms sometimes form along a cold front.

Occluded Front
- These occur when a fast moving cold front overtakes a warm front and lifts the warm air away from the surface. Occluded fronts contain the worst features of both warm and cold fronts: turbulent flying conditions, showers and/or continuous precipitation, poor visibility and broad geographic extent.

Stationary Fronts - If air masses maintain their warm/cold identity but don't exert any displacement force, a stationary front is formed. The associated weather with these fronts cover a large geographic area