OVERRUNNING MEANS A DAMP SATURDAY

A wedge of shallow heavier cool air is moving in behind a cold front Thanksgiving evening. We will notice drier and cooler weather Friday. But rain is in the forecast Saturday as warm air tries to move back north. This overrunning will result in mostly cloudy skies and light showers increasing through the afternoon. This .gif file from the University of Illinois shows the process. Assume Point A is Miami and B is Jacksonville.



Overruninng is the result of a physical process of isentropic lift: Warmer air (point A) is moved northward due to large scale lifting weather systems. Typically this is due to spinning pockets of air at 18,000 ft. Bends or dips in the Jet stream impart the spin to the vorticity maxims. Warm air is lighter and rides over denser colder air (point B). The air glides upwards until it cools and the humidity condenses out falling as light rain.