front science definition

The boundary between two air masses that have different temperatures or humidity. In the mid-latitude areas of the Earth, where warm tropical air meets cooler polar air, the systems of fronts define the weather and often cause precipitation to form. Warm air, being lighter than cold air, tends to rise, cool, and condense along such boundaries, forming rain or snow. See also cold front, occluded front, polar front, stationary front, warm front.