1. Air Masses and Fronts

2. Air Mass A large body of air A large body of air At least 1,000 miles across At least 1,000 miles across Uniform temperature and humidity Uniform temperature and humidity Flows as one unit Flows as one unit

3. Air Mass Four main types Four main types –Cold (polar) –Warm (tropical) –Water (maritime) –Land (continental) Combinations Combinations –Maritime tropical –Maritime polar –continental tropical –Continental polar

4. Fronts When two air masses meet When two air masses meet

5. Fronts Warm front—When a warm air mass overrides a cold area, it rises slowly, creating nimbostratus, altostratus or cirrostratus clouds. This can produce light precipitation. Warm front—When a warm air mass overrides a cold area, it rises slowly, creating nimbostratus, altostratus or cirrostratus clouds. This can produce light precipitation.

6. Fronts Cold front—When a cold air mass overrides a warm area, it pushes the warm air up forcefully, creating cumulus and cumulonimbus clouds. Cold fronts often produce thunderstorms and very bad weather. Cold front—When a cold air mass overrides a warm area, it pushes the warm air up forcefully, creating cumulus and cumulonimbus clouds. Cold fronts often produce thunderstorms and very bad weather.

7. Fronts Stationary front— When a cold air mass and warm air mass flow side-by-side, and neither mass invades the other, weather can by unpredictable. It most often resembles a warm front, with light rain if any precipitation occurs. Stationary front— When a cold air mass and warm air mass flow side-by-side, and neither mass invades the other, weather can by unpredictable. It most often resembles a warm front, with light rain if any precipitation occurs.

8. Fronts Occluded front— When two cold air masses trap a warm air mass, they push the warm air up. The boundary that exists is between two similar air masses: cold and cooler air. Clouds and precipitation are likely. Occluded front— When two cold air masses trap a warm air mass, they push the warm air up. The boundary that exists is between two similar air masses: cold and cooler air. Clouds and precipitation are likely.

9. Mid-latitude Cyclones Severe storms that develop between tropical and polar air masses in mid- latitude regions around low-pressure centers. Severe storms that develop between tropical and polar air masses in mid- latitude regions around low-pressure centers.