1. what causes air masses movement?
2. what causes the warm air ahead of a cold front to rise?
3. what kind of clouds usually form in a cold front?
4. what wind direction change usually occurs as a cold front moves through an area?

Air masses move mainly due to the drag and influence of the upper level air currents also known as jet streams. Warm air rises ahead of a cold front because cold air is denser than warm air. Cloud fronts are typically formed by warm fronts and cold fronts. In the Northern Hemisphere, the passage of a cold front usually means a change in wind direction from a south-southwesterly direction to a west-northwesterly direction.

Explanation:

The Jet streams are bands of high speed winds located in the upper atmosphere that typically reside between cells of atmospheric circulation. There are two types of jets, polar and subtropical. The polar jet is far more energetic since the temperature gradient between the pole and the subtropical regions is great than that between the Tropics and Subtropics.As warm air rises it cools. The cooling action at some point in the rising process will cause the warm air to reach the condensation point. At this point, clouds begin to form. In this way fronts produce rain and storms. The strong the front, the more convective active is involved. The best conditions for strong storm formation involve the collision of a potent cold front with a mass of warm, moist air. Both warm fronts and cold fronts produce cloud fronts, but the types of clouds are different. Cold fronts are more likely to produce vertically-developed clouds like cumulonimbus, whereas warm fronts are usually accompanied by lower and flatter stratus-type clouds. The lack of vertical development brought by warm fronts can be explained by the fact that warm fronts do no force cold air to rise over them. Rather, the warm air overrides the cold air and displaces it little by little.This change in wind direction, which is reversed in the Southern Hemisphere, is due to the direction of the prevailing winds that control each air mass. In the case of North America, maritime tropical air masses arrive out of the Southeast and the Gulf of Mexico. Continental polar air masses arrive from the North or Northeast on their journey from Canada and the polar regions.