17.1 – Air Masses and Fronts

1. 17.1 – Air Masses and Fronts An air mass is a huge body of air that has similar temperature, humidity, and air pressure throughout.

2. Types of Air Masses • Scientists classify air masses according to temperature and humidity. • There are four major types of air masses that influence weather in N. America.

3. Maritime Tropical – • Warm, humid air masses that form over the oceans and Gulf of Mexico • They travel up from the south bringing warm, humid air.

4. Bring showers and thunderstorms in the summer. • Bring snow in the winter.

5. 2. Maritime Polar • Cool, humid air masses that form over the North Pacific and Atlantic Oceans. • They affect the West Coast more than the East Coast.

6. They bring rain, and cool temps to the west coast.

7. 3. Continental Tropical • Hot, dry air masses that form only in summer over areas in the SW U.S. and N. Mexico. • They move NE, bringing hot dry weather.

8. 4. Continental Polar • Large air masses that form over N. Canada and Alaska. • Bring cool, dry air to much of North America.

9. FRONTS • As huge masses of air move across land and water, they bump into each other.

10. When 2 masses with different temps and density collide, they do not mix. • The area where the air masses meet and do not mix becomes a “front”

11. A front forms because one air mass is less dense than the other air mass. • There are 4 types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

12. Cold Fronts

13. Cold fronts form when a rapidly moving cold air mass runs into a slowly moving warm air mass. • Often results in the formation of clouds, rain, and/or snow. • Also, thunderstorms.

14. Warm Fronts • Forms when a rapidly moving warm air mass collides with a cold air mass. • Can cause rain or fog. • Slower moving than cold front.

16. Stationary Fronts • Forms when a warm air mass and a cold air mass meet and no movement occurs. • Neither air mass has enough force to move the other.

17. Occluded Front • Forms when a warm air mass is caught between two cooler air masses. • The warm air mass gets lifted and cut off from the ground by the two cooler air masses.

18. 17.2 - Storms A swirling center of low air pressure is called a cyclone. As warm air at the center of the cyclone rises, cooler air blows toward this from areas with higher pressure.

19. The winds swirl in a counter-clockwise fashion b/c of the Coriolis Effect. • Cyclones and low pressure areas are associated with storms and precipitation.

21. Anticyclones are the opposite of cyclones. • They are areas of high pressure that are associated with dry and clear weather. • Air blows from high pressure areas to low pressure areas.

22. Kinds of Storms • A storm is a violent disturbance in the atmosphere. • Storms involve sudden changes in air pressure, which cause rapid air movements.

23. Hurricanes • A hurricane is a tropical storm that has winds of 74mph or greater. • They begin over warm water as a low pressure area.

24. The center of a hurricane is a ring of clouds surrounding a quiet “eye” • When the eye arrives, the winds grow calm and the sky may clear.

26. Hurricanes can last for over a week. • They get their energy from the warm, humid air at the ocean’s surface. • When they get over land, they begin to lose energy.

27. Tornadoes • Tornadoes form in low, heavy cumulonimbus clouds. • They form when cold, dry air mass from Canada collides with a warm, humid air mass from the Gulf of Mexico.

28. During a tornado, the safest place to be is in the basement of a well-built building.