Weather Fronts

A front is the boundary between two air masses of different properties.  Those differences usually involve both temperature and atmospheric moisture content.  Differences across a frontal boundary may range from large to barely measurable; in fact, "frontolysis" or the dissipation of a front occurs as those differences evolve and become immeasurably small.  A "strong front" is one with relatively large differences across the frontal boundary; a "weak front" is one with relatively small differences. 

Fronts may be stationary or in motion.  A stationary front is called by that name, "stationary front."  A moving front is named "cold front" if a colder air mass is displacing a warmer air mass, "warm front" if a warmer air mass is displacing a colder air mass and "occluded front" where a faster moving cold front has overtaken a slower moving warm front, resulting in a boundary, usually aloft, where all three air masses are in contact. 

Fronts may or may not be associated with cloud formation and stormy weather.  The stronger the front is, the greater the probability of associated stormy weather.  Fronts are often associated with and connected to mid-latitude cyclones.