Air Masses and Fronts

Air masses and fronts have an effect on the weather throughout the world, affecting everyone everywhere. An air mass is a large region of the atmosphere containing a volume of air defined by its temperature and moisture content. In an air mass the temperatures and amount of moisture is about the same throughout the region.

There are different air masses throughout the world which mostly control the weather in that region. In the United States, global winds tend to move air masses from east to west. When different air masses come together and meet the boundary is called a front. The air masses do not mix together. A front is the narrow area or boundary where the air masses meet. Along this front is where the weather changes most rapidly.

There are two fronts to be most familiar with and which are heard of most often. A cold front and a warm front. A cold front occurs at a warm air mass where the weather changes as cold air moves in. A warm front occurs when warm air moves over a cold air mass. Fog may also be a result of a warm front moving into a cold air mass.

Another type of front also involves a cold front and a warm front. An occluded front occurs when a cold front overtakes a warm front. When this happens the warm air is separated at the Earth's surface. When an occluded front occurs it is most likely lead to precipitation such as rain, snow, sleet, or hail, depending on the air temperature and season of the year. After the cold front passes though, the temperatures will usually begin to get warmer again.

One final type of front is called a stationary front. A stationary front occurs when a cold air mass and a warm air mass meets. There is usually a drastic temperature change before the cold and warm air masses meet as well as a change in the direction of the wind. The stationary front may also stay over an area for days or weeks, or sometimes even longer. It is not moving and the weather it brings changes very little.

On a weather map the different fronts are shown by different symbols and colors. A cold front is represented by a blue line with triangles pointing toward the direction of movement. A warm front is represented as a red line with half circles pointing toward the direction of movement. A stationary front is represented as an alternating warm and cold front symbol. An occluded front is represented as a purple line with teeth and half circles.

In summary, an air mass is a large region of the atmosphere containing a volume of air defined by its temperature and moisture content. When the air masses come together, the boundary between them is called a front. The four types of fronts include cold fronts, warm fronts, occluded fronts and stationary fronts. Cold and warm fronts bring cold and warm air, an occluded front is when a cold front takes over a warm front. Finally, a stationary front occurs when cold and warm air masses come together stays in one place for a short or long period of time. On weather maps there are different colors and symbols used to identify each of the fronts. The colors used include blue, red, and purple, along with lines, triangles, and half circles. The weather throughout the world is the result of air masses, cold fronts, and warm fronts.