weather patterns air mass: a large body of air that has properties similar to the part of earth’s...
TRANSCRIPT
Weather PatternsWeather Patterns• Air Mass: A large
body of air that has properties similar to the part of Earth’s surface over which it develops.
• Air masses cover thousands of square miles.
• Six major air masses affect weather in the Unites States.
High Pressure
•Winds blow away from a center of high pressure.
•These winds spiral clockwise in the northern hemisphere.
•High-pressure areas are associated with fair weather and are called anticyclones.
Low Pressure
•Winds blow into a low-pressure area in the northern hemisphere and swirl in a counter-clockwise direction.
•Low pressure systems are called cyclones and are associated with stormy weather.
Weather PatternsWeather Patterns•Air pressure is measured using a barometer.
•Weather has high- and low-pressure systems.
•Winds blow from areas of high to areas of low pressure.
Weather PatternsWeather Patterns
• Low pressure systems at Earth’s surface are regions of rising air.
• Clouds form when air is lifted and cools.
• Areas of low pressure usually have cloudy weather.
• Sinking motion in high-pressure air masses makes it difficult for air to rise and clouds to form.
• That’s why high pressure usually means good weather.
Weather Patterns: FrontsWeather Patterns: Fronts
• A boundary between two air masses of different density, moisture, or temperature is called a front.
• Cloudiness, precipitation, and storms sometimes occur at frontal boundaries.
• Four types of fronts include cold, warm, occluded, and stationary.
A cold front forms when a mass of cold air meets & pushes warm air up rapidly.. Violent storms are associated with a cold front. Fair, cool weather usually follows.
Cold Front
A warm front forms when a mass of warm air overtakes a cold air mass and moves over it. Rain and showers usually accompany a warm front. Hot, humid weather usually follows.
Warm Front
When a cold front overtakes a warm front, an occluded front forms.
As the warm air is pushed upward, the cold air meets cool air. An occluded front may also occur when cool air overtakes a cold front and warm air is pushed upward. An occluded front produces less extreme weather than a cold or warm front.
Occluded Front
When a warm air mass meets a cold air mass and no movement occurs, a stationary front forms. Rain may fall in an area for many days when a stationary front is in place.
Stationary Front
Weather Patterns: Severe Weather Patterns: Severe WeatherWeather• Thunderstorms can stall over
a region, causing flash flooding.
• Flash floods can occur with little warning.
• Strong Winds >89mph are classified as severe.
• Hail can destroy property and farm crops.
• Lightning
• Tornadoes
Weather Patterns: LightningWeather Patterns: Lightning• In a storm cloud, warm air is lifted rapidly as cooler air
sinks. This movement of air causes different parts of the cloud to become oppositely charged.
• When current flows between regions of opposite electrical charge, lightning flashes.
•occurs within clouds, b/w clouds, or from cloud to ground.
•Thunder results from rapid heating of air around a bolt of lightning. Temperature can reach 30,000°C!
•The extreme heat causes air around the lightning to expand rapidly, then quickly cools and contracts.
•rapid movement of molecules form sound waves heard as thunder.
•Thunder-snow video, click here
• Hail Video – click here
Weather Patterns: TornadoesWeather Patterns: Tornadoes• Tornado: A violently rotating column of air in contact
with the ground.
• Wind Shear: Wind at different heights blows in different directions and at different speeds. This can create a rotating column parallel to the ground.
• Updraft tilts the rotating column upward into the thunderstorm creating a funnel cloud.
• If the funnel comes into contact with the ground, it is called a tornado.
• Although tornadoes rarely exceed 200m in diameter and usually last only a few minutes, they often are extremely destructive.
2011 EF5 Joplin TornadoHow a tornado forms!
Moore Tornado 2013
Weather Patterns: HurricanesWeather Patterns: Hurricanes• Steered by surface winds, they can travel west, gaining
strength from the heat and moisture of warm ocean water.
• Damage: High winds, tornadoes, heavy rains, lightning, high waves, and flooding can destroy crops, demolish buildings, kill people and animals.
• When over water, the warm, moist air rises and provides energy for the storm.
• When it reaches land, its supply of energy disappears and the storm loses power.
Weather Patterns: BlizzardsWeather Patterns: Blizzards
The National Weather Service classifies a winter storm as a blizzard if:
1.The winds are 56 km/h.
2.The temperature is low.
3.The visibility is less than 400 m in falling or blowing snow.
4.These conditions persist for three hours or more.
Severe Weather SafetySevere Weather Safety• When severe weather threatens, the National Weather
Service issues a watch or warning.
• Watches are issued when conditions are favorable for severe thunderstorms, tornadoes, floods, blizzards, and hurricanes.
• METEROLOGISTS ARE ASKING YOU TO WATCH AND SEE WHAT WEATHER MAY FORM.
• When a warning is issues, severe weather conditions already exist.
• THEY ARE WARNING YOU TO GET AWAY FROM THE DANGEROUS WEATHER!!!
• You should take immediate action.