An air mass is any large volume of air having a relatively uniform temperature and water vapor content. A front is simply the boundary between two air masses. When a cold air mass pushes into a warm airmass, we call the boundary a Cold Front. When the warm air pushes forward, we call the boundary a Warm Front.
Cold fronts typically come from the north and move in a southerly direction. They tend to pass quickly, usually within a few hours. As a cold front passes, it plows under the existing warmer air rapidly lifting it and often times generating thunderstorms.All pilots should be very cautious when flying in pre cold frontal conditions. Beginning pilots should wait for the front to pass.
Post cold frontal conditions are generally unstable and great for soaring.
Warm fronts typically come from the south and move northwest. They move more slowly sometime staking several days to pass. The less dense and therefore lighter air tends to ride up and over the already present cooler air mass.
Because of the slow movement of a warm front, it is often possible to predict its approach a day or two in advance by noting a gradual increase and lowering of the clouds as illustrated below.
The passage of a warm front is not typically a good time to fly.