2. Front The boundary between two adjoining air masses having contrasting characteristics.
3. Warm Front A front along which a warm air mass overrides a retreating mass of cooler air.
4. Cold Front A front along which a cold air mass thrusts beneath a warmer air mass.
5. Stationary Front A situation in which the surface position of a front does not move; the flow on either side of such a boundary is nearly parallel to the position of the front.
6. Occluded Front A front formed when a cold front overtakes a warm front; it marks the beginning of the end of a middle-latitude cyclone.
7. Key Concept When two air masses meet, they form a front, which is a boundary that separates two air masses.
8. Key Concept A warm front forms when warm air moves into an area formerly covered by cooler air.
9. Key Concept A cold front forms when cold, dense air moves into a region occupied by warmer air.
10. Key Concept In such cases, the surface position of the front does not move, and a stationary front forms.
11. Key Concept When a active cold front overtakes a warm front, an occluded front forms.
12. Key Concept Middle-latitude cyclone are large centers of the low pressure that generally travel form west to east and cause stormy weather. More often than not, air high up in the atmosphere fuels a middle-latitude cyclone.
