Low Pressure Systems vs High Pressure Systems

Let’s Compare Low Pressure Systems (L) High Pressure Systems (H)

Look!!! Convecting air…

LOW PRESSURE SYSTEMS Low pressure systems involve air that tends to rise, thus causing clouds and precipitation. Those near the equator tend to be high energy due to strong ground heating (convectional). Low pressure systems may develop tornadoes and sometimes develop into hurricanes, fuelled by warm, very humid air evaporated from tropical oceans in summer. They tend to be fast moving, with plenty of cloud cover that reduces temperature range, strong winds and high rainfall.

LOW PRESSURE SYSTEMS Hurricane off USA fueled by hot humid air over the Caribbean

LOW PRESSURE SYSTEMS A convectional cumulonimbus cloud results from strong ground heating at the equator

LOW PRESSURE SYSTEMS A tornado may develop from a cumulonimbus cloud

HIGH PRESSURE High Pressure means that air tends to sink. Sinking air is compressed, warms up as a result and its relative humidity falls below saturation. Any clouds evaporate. Rainfall is unlikely.

CLEAR SKIES CAUSE FROST HIGH PRESSURE � High pressure systems have clear skies, varying winds, little rainfall. � Visibility is typically good � Cloud cover is slight, resulting in a high ranges of temperature (hot days, cold nights). FEW CLOUDS VISIBLITY REMAINS BETTER IN MOUNTAINS - LESS POLLUTION CLEAR SKIES LITTLE WIND

Weather Fronts Teacher Page

MAP TAP Weather Fronts 11 Air Mass A large body of air with similar temperature and moisture. A large body of air with similar temperature and moisture. Air masses form over large land or water masses. Air masses form over large land or water masses.

MAP TAP Weather Fronts 12 Frontal Boundaries Where air masses interact – also know as a front. Where air masses interact – also know as a front. 4 kinds of fronts: 4 kinds of fronts: –Cold front –Warm front –Occluded front –Stationary front

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. Back to activity

Cold Front Thunderheads can form as the moisture in the warm air mass rises, cools, and condenses. As the front moves through, cool, fair weather is likely to follow. Thunderheads can form as the moisture in the warm air mass rises, cools, and condenses. As the front moves through, cool, fair weather is likely to follow. Back to activity

MAP TAP Weather Fronts 15 Warm Front Warm air mass replacing a cooler air mass. Warm air mass replacing a 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. Back to activity

MAP TAP Weather Fronts 16 Warm Front As the warm air mass rises, it condenses into a broad area of clouds. A warm front brings gentle rain or light snow, followed by warmer, milder weather. As the warm air mass rises, it condenses into a broad area of clouds. A warm front brings gentle rain or light snow, followed by warmer, milder weather. Back to activity

MAP TAP Weather Fronts 17 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 (after the front has passed). The weather activity in a cold front is often violent and happens directly at the front (after the front has passed). Cold fronts have sudden gusty winds high in the air creating turbulence. Cold fronts have sudden gusty winds high in the air creating turbulence. In a warm front the cloud formation is very low (altitude wise) often creating situations of poor visibility. In a warm front the cloud formation is very low (altitude wise) often creating situations of poor visibility.

MAP TAP Weather Fronts 18 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. Back to activity

MAP TAP Weather Fronts 19 Occluded Fronts The temperature drops as the warm air mass is occluded, or “blocked,” from the ground and pushed upward. Can bring strong winds and heavy precipitation. The temperature drops as the warm air mass is occluded, or “blocked,” from the ground and pushed upward. Can bring strong winds and heavy precipitation. Back to activity

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. Back to activity

MAP TAP Stationary Fronts Where the warm and cold air meet, clouds and fog form, and it may rain or snow. Can bring many hours or days of clouds and precipitation. Where the warm and cold air meet, clouds and fog form, and it may rain or snow. Can bring many hours or days of clouds and precipitation. Back to activity

Locate the 4 types of fronts on this weather map. Hint 1 Hint 2 Hint 3 Hint 4

Cold Fronts

Warm Front

Stationary Front

Occluded Front

Weather Fronts 27 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.

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

MAP TAP Weather Fronts 29 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.

MAP TAP Weather Fronts 30 Summary Describe the 4 types of fronts and the weather associated with each front. Describe the 4 types of fronts and the weather associated with each front.