Air Masses and Fronts

I. Types of Air Masses air mass- huge body of air that has similar temp, humidity, and air pressure at any given height. Scientists classify them according to their temperature and humidity. Four Types- 1. Maritime tropical 2. Continental tropical 3. Maritime polar 4. Continental polar

Maritime- wet or humid Continental- dry Polar- cold (high pressure-many of air molecules) Tropical- warm (low pressure- few air molecules)

A. Maritime Tropical 1. Warm, humid air masses that form over tropical oceans. 2. Mainly on west coast. 3. Summer- hot, humid weather 4. Winter- heavy rain or snow.

B. Maritime Polar Cool, humid air mass formed over icy cold North Pacific and North Atlantic oceans. Summer- cool, humid air. Fog, rain and cool temps occur.

C. Continental Tropical Hot, dry air masses form mostly in summer over dry areas of SW and northern Mexico.

D. Continental Polar Cold, dry air mass formed near Arctic Circle. Bring bitter, cold weather with very low humidity. Winter- brings clear, cold, dry air.

II. How Air Masses Move In the USA, air masses are moved from west to east by the a. prevailing westerlies b. jet streams- they carry air masses along. 2. Fronts- boundary where air masses meet. Storms and changeable weather develop there.

III. Types of Fronts Cold front- 1. fast moving cold air mass runs into slow moving warm air mass. 2. Denser, cold air slides under lighter warm air. 3. warm air is pushed up. 4. resulting weather- cloudy skies or precipitation.

Cold Front

B. Warm front Fast moving warm air mass overtakes a slowly moving cold air mass. Cold air is denser, so warm air moves over cold air. Warm air fronts move slowly, so it may be rainy or cloudy for days. Resulting weather- clouds and precipitation.

Warm Front

Teach your neighbor what happens in a cold front and a warm front Teach your neighbor what happens in a cold front and a warm front. Include what kind of weather it creates.

Draw a picture of a cold front and a warm front. You have 1 min Draw a picture of a cold front and a warm front. You have 1 min. for each pic.

C. Stationary Front Cold and warm air masses meet, but neither can move. They have a “standoff”. Resulting weather- many days of clouds and precip.

Stationary Front

D. Occluded Fronts Warm air mass is caught btwn two cooler air masses. Denser cool air masses move under the less dense warm air mass and push warm air upward. Two cooler air masses meet in the middle and may mix. Temp near ground becomes cooler. Warm air mass is cut off from ground. Resulting weather- cloudy and rain or snow.

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Occluded Front

Teach your neighbor what happens in a stationary front and an occluded front. Include the weather they create.

Draw a picture of a stationary front and an occluded front Draw a picture of a stationary front and an occluded front. You have 1 min. for each pic.

IV. Cyclones and Anticyclones Cyclone- swirling center of low air pressure. “L” on a weather map means low pressure. Winds spiral in toward the center of the system. Moves counterclockwise in N. Hem. Air rises in a cyclone, air cools forming clouds and precip. Causes clouds, wind, and precip.

Anticyclones Anticyclones- high pressure centers of dry air. Usually called “highs- “H” on a weather map. Winds spiral outward from the center, moving towards areas of low pressure. Moves clockwise in N. Hem. Causes dry, clear weather

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