Air Pressure and Fronts

1. Air Pressure and Fronts

2. Air Pressure • Air has weight, and is in constant motion and is pulled towards Earth’s center by gravity. • Air pressure is greatest at the Earth’s surface and decreases with increased altitude. • Higher air pressure near the ground.

3. What instrument is used to measure air pressure? • Barometer measures air pressure. • High pressure indicates Dry Air • Low pressure indicates Moist air

4. Fronts Fronts occur where two large air masses collide at the earth’s surface. Each air mass has a different temperature associated with it. In the US, air masses usually travel west to east.

6. Types of Air Masses • Continental Polar • Maritime Polar • Maritime Tropical • Continental Tropical

7. Airmasses do not usually mix. The boundary between colliding air masses is called a front. • Fronts are usually associated with some form of precipitation. • Thunderstorms, tornadoes, and other severe weather can occur with fronts.

9. Four types of fronts • Cold Front • Warm Front • Stationary Front • Occluded Front Why are there no fronts in the Tropics? There are no cold air masses, just warm air.

10. Cold Front • Heavy cold air displaces lighter warm air, pushing it upward. • Cumulus clouds. • Thunderstorms occur. • Temperatures drop5 to 15 degrees. • Winds are gusty. • Rain, snow, sleet, and hail can occur.

11. COLD FRONT

13. Warm Front • Warm fronts occur when warm air replaces cold air by sliding over it. • Altocumulus clouds form • Less chance of rain, snow, or sleet. • Temperatures may increase. • Winds are usually gentle.

14. Warm Front

16. Stationary Front • Neither warm nor cold air advances. Neither front is moving. • Lasts for days. Lots of clouds • Temperatures remain the same. • Gentle or no wind.

18. Occluded Front • Fast-moving cold air mass overtakes a slower-moving cold air mass and forces it up. • Cool temperatures and large amounts of precipitation.