Objective: Determine the humidity and temperature of air masses

Air Masses and Fronts Science 7 th Grade

MAP TAP Weather Fronts 3 Air Mass A large body of air with similar temperature, humidity, and air pressure. A large body of air with similar temperature, humidity, and air pressure. Air masses form over large land or water masses. Air masses form over large land or water masses.

Air masses are classified based on their and amount of

Whether an air mass is warm or cold depends on the temperature over which the mass forms. Whether an air mass is warm or cold depends on the temperature over which the mass forms. 4 types of air masses 4 types of air masses 1. Tropical – warm air masses that form over the tropics. 2. Polar – cold air masses that form over the poles. 3. Maritime – air masses that form over the ocean (very humid) 4. Continental – form over land – (are dry) MAP TAP Weather Fronts 5

Continental - Means land. Means land. A Continental air mass forms over land. A Continental air mass forms over land. Weather Fronts 6

Maritime - Means water. Means water. Maritime air masses form over water. Maritime air masses form over water. MAP TAP Weather Fronts 7

Polar Polar means it forms over the poles. Polar means it forms over the poles. COLD! COLD! MAP TAP Weather Fronts 8

Tropical Form over the tropics (near the equator) Form over the tropics (near the equator) WARM!! WARM!! MAP TAP Weather Fronts 9

MAP TAP Weather Fronts 10

The abbreviations used to classify air masses use the following letters: c, m, T, P, and A. For each letter, describe its property: WordMeans c m T P continentaldry maritimemoist Tropicalwarm Polarcold

warm and moistcold and dry

Why is the middle of the globe red?

mT air mass warm, moist air Low Pressure Center cP air mass dry, cool air High Pressure Area

mT air mass warm, moist air Low Pressure Center cP air mass dry, cool air High Pressure Area

mT air mass warm, moist air Low Pressure Center cP air mass dry, cool air High Pressure Area

mT air mass warm, moist air Low Pressure Center cP air mass dry, cool air High Pressure Area

mT air mass warm, moist air Low Pressure Center cP air mass dry, cool air High Pressure Area

MAP TAP Weather Fronts 23 Fronts Fronts Where air masses meet but do not mix due to different temperatures and densities. it becomes a front Where air masses meet but do not mix due to different temperatures and densities. it becomes a front

Fronts 4 kinds of fronts: 4 kinds of fronts: –Cold front –Warm front –Occluded front –Stationary front MAP TAP Weather Fronts 24

Cold Front A cold air mass is replacing a warmer air mass. A cold air mass is replacing a warmer air mass. Shown on a weather map by a blue line with triangles pointing the direction the cool air is moving. Shown on a weather map by a blue line with triangles pointing the direction the cool air is moving.

Cold Front Cold Front Rapidly moving cold air mass runs into a slowly moving warm air mass. Rapidly moving cold air mass runs into a slowly moving warm air mass. The denser cold air slides under the lighter warm air pushing it upward. The denser cold air slides under the lighter warm air pushing it upward. The rising air cools and condenses, forming clouds. The rising air cools and condenses, forming clouds. Heavy rain or snow may fall. Heavy rain or snow may fall. If the warm air mass contains only a little water vapor, there may be only cloudy skies. If the warm air mass contains only a little water vapor, there may be only cloudy skies. MAP TAP Weather Fronts 26

Cold Front Cold Front Cold fronts move quickly and can cause abrupt weather changes including violent thunderstorms Cold fronts move quickly and can cause abrupt weather changes including violent thunderstorms After a cold front passes through, cool, dry air moves in. After a cold front passes through, cool, dry air moves in. Clear skies and cooler temperatures often follow. Clear skies and cooler temperatures often follow. MAP TAP Weather Fronts 27

NSF North Mississippi GK-8 Fronts: Four Types of Fronts 1. Cold Front: The zone where cold air is replacing warmer air Air gets drier after a cold front moves through

MAP TAP Weather Fronts 29 Warm Front Warm air mass collides with a slowly moving cooler air mass. Warm air mass collides with a slowly moving cooler air mass. Shown on a weather map by a red line with half circles pointing the direction the warm air is moving. Shown on a weather map by a red line with half circles pointing the direction the warm air is moving.

Warm Front Warm Front Moving warm air mass collides with a slowly moving cold air mass. Moving warm air mass collides with a slowly moving cold air mass. The warm air moves over the denser cold air. The warm air moves over the denser cold air. If the warm air is humid, showers and light rain fall along the front where the warm and cold air meet. If the warm air is humid, showers and light rain fall along the front where the warm and cold air meet. If the warm air is dry scattered clouds form. If the warm air is dry scattered clouds form. MAP TAP Weather Fronts 30

NSF North Mississippi GK-8 Fronts: Four Types of Fronts 2. Warm Front: The zone where warm air is replacing colder air Air gets more humid after a warm front moves through

Warm Front Warm Front Because warm fronts move more slowly than cold fronts, the weather may be rainy or foggy for several days. Because warm fronts move more slowly than cold fronts, the weather may be rainy or foggy for several days. After the warm front passes, the weather is likely to be warm and humid. After the warm front passes, the weather is likely to be warm and humid. In winter, warm fronts bring snow. In winter, warm fronts bring snow. MAP TAP Weather Fronts 32

MAP TAP Weather Fronts 33 Comparing Warm and Cold Fronts Cold fronts move faster than warm fronts. Cold fronts move faster than warm fronts. The weather activity in a cold front is often violent and happens directly at the front. The weather activity in a cold front is often violent and happens directly at the front. Cold fronts have sudden gusty winds high in the air creating turbulence. Cold fronts have sudden gusty winds high in the air creating turbulence. The weather activity in a warm front generally happens before the front passes. The weather activity in a warm front generally happens before the front passes. In a warm front the cloud formation is very low often creating situations of poor visibility. In a warm front the cloud formation is very low often creating situations of poor visibility.

MAP TAP Weather Fronts 34 Occluded Fronts When a warm front is trapped by 2 cold fronts. When a warm front is trapped by 2 cold fronts. Shown on a weather map by a purple line with alternating triangles and semicircles pointing the direction the front is moving. Shown on a weather map by a purple line with alternating triangles and semicircles pointing the direction the front is moving.

Occluded Fronts Occluded Fronts A warm air mass is caught between two cooler air masses. A warm air mass is caught between two cooler air masses. The denser cool air masses move underneath the less dense warm air and push it upward. The denser cool air masses move underneath the less dense warm air and push it upward. The temperature near the ground becomes cooler. The temperature near the ground becomes cooler. MAP TAP Weather Fronts 35

Occluded Fronts Occluded Fronts MAP TAP Weather Fronts 36 The warm air mass is cut off, or occluded, from the ground. The warm air mass is cut off, or occluded, from the ground. As the warm air cools and its water vapor condenses, the weather may turn cloudy and rainy or snowy. As the warm air cools and its water vapor condenses, the weather may turn cloudy and rainy or snowy.

NSF North Mississippi GK-8 Fronts: Four Types of Fronts 3. Occluded Front: Formed when a cold front overtakes a warm front This occurrence usually results in storms over an area In U.S., the colder air usually lies to the west

MAP TAP Stationary Fronts A front that stops moving or is moving very slowly. A front that stops moving or is moving very slowly. Shown on a weather map with alternating red semicircles pointing away from the warm air and blue triangles pointing away from the cold air. Shown on a weather map with alternating red semicircles pointing away from the warm air and blue triangles pointing away from the cold air.

Stationary Fronts Stationary Fronts Sometime cold and warm air masses meet, but neither has enough force to move the other. Sometime cold and warm air masses meet, but neither has enough force to move the other. They meet in a “standoff” They meet in a “standoff” MAP TAP Weather Fronts 39

Stationary Fronts Where the warm and cool air meet, water vapor in the air condenses into rain, snow, fog, or clouds. Where the warm and cool air meet, water vapor in the air condenses into rain, snow, fog, or clouds. It may stall over an area and bring many days of clouds and precipitation. It may stall over an area and bring many days of clouds and precipitation. MAP TAP Weather Fronts 40

NSF North Mississippi GK-8 Fronts: Four Types of Fronts 4. Stationary Front: When either a cold or warm front stops moving When the front starts moving again it returns to either being a cold or warm front

Locate the 4 types of fronts on this weather map.

Cold Fronts

Warm Front

Stationary Front

Occluded Front

Weather Fronts 47 Be a Weather Forecaster You are planning to travel to Alabama in 2 days. The high temperature there for today is 68 º F. Use the map to help you predict whether the temperature in Alabama will increase, decrease, or stay the same. Explain why you think so.

48 Be a Weather Forecaster There is a cold front approaching. The temperatures will probably be cooler behind the front.

MAP TAP Weather Fronts 49 Be a Weather Forecaster Of course, meteorologists (weather forecasters) use much more data than fronts and air masses to help them forecast the weather more accurately. But any forecast is just a prediction of what might happen. Even with the best data, weather forecasts can be wrong. Of course, meteorologists (weather forecasters) use much more data than fronts and air masses to help them forecast the weather more accurately. But any forecast is just a prediction of what might happen. Even with the best data, weather forecasts can be wrong.