The motion of air mass motion is usually based upon the air flow in the upper atmosphere. As the jet stream changes intensity and position, it affects the motion and strength of air masses. Where air masses converge, they form boundaries called "fronts".

3-D view of a cold front.

Fronts are identified by change of temperature based upon their motion. With a cold front, a colder air mass is replacing a warmer air mass. A warm front is the opposite affect in that warm air replaces cold air. There is also a stationary front, which, as the name implies, means the boundary between two air masses does not move.

The motion of air masses also affects where a good portion of precipitation occurs. The air of cold air masses is more dense than warmer air masses. Therefore, as these cold air masses move, the dense air undercuts the warmer air masses forcing the warm air up and over the colder air causing it to rise into the atmosphere.

So, fronts just don't appear at the surface of the earth, they have a vertical structure or slope to them as well. Warm fronts typically have a gentle slope so the air rising along

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2 years ago