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Air Masses:

Air masses are large bodies of air that take on temperature and moisture that classifies them by the region they are formed in. Such as a continental polar air mass is formed over, the Polar Regions, which brings cool dry air. Another example of an air mass is a maritime air mass that forms over warm tropical waters, which brings warm moist air.

As an air mass passes over a warm surface convective currents form which cause the air to rise. An unstable air mass is created which bring good visibility, cumulus clouds, showers, and turbulence.

On the opposite side, as an air mass passes over a cold surface, no convective currents are formed. This creates a stable air mass to form bring poor visibility, ad low stratus clouds or fog.


As two different air masses meet with each other over water or land, the line between the two different types of air masses is called a front.

When a front is approaching an area, it is a sign that the weather is going to change.

There are four types of fronts:

  • Warm

  • Cold

  • Stationary

  • Occluded

Warm fronts

Warm fronts usually replace a cold front and bring warm air. Prior to the warm front arriving cirriform clouds or stratiform clouds, and fog will be present.

Thunderstorms are associated with warm fronts during the summer. If the warm front slows down, it can cause several days with low visibility and IFR conditions.

Cold fronts

Cold fronts are cold dense air masses pushing warm air masses upward and away. Remember cold air is denser and replaces warm less dense air.

Cold fronts bring cumulus and cumulonimbus clouds. They are also associated with squall lines, thunderstorms, turbulence along the frontal line.

Stationary fronts

These fronts are actually two different air masses a cold and warm air mass pushing and pulling, which causes it to stop moving across the surface.

This front can bring thunderstorms. Stratus clouds and light precipitation or drizzle with calm winds are most common and can cover a large area with IFR conditions.

Occluded fronts

These fronts are unstable and not fun for flying. Occluded fronts are a combination of two fronts over the same area. Two fronts catch up and overtake a warm front. One front is near the surface and the other front is aloft or right on top.

Since they are unstable fronts, they are associated with clouds, precipitation, thunderstorms. Thunderstorms might be embedded within clouds.

Chart symbols

The symbols for all four fronts are found on surface analysis charts.


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