a large body of air that has the same temperature and humidity throughout classified according to where they originate during the time the air mass is over an area, it determines the weather of that area

Originates over the ocean  humid air mass (m) (maritime)

Originates over the land  dry air mass (c) (continental)

Originates in cold air  cool air mass (P) (Polar)

Originates in warm air  warm air mass (T) (Tropical)

Maritime Tropical Atlantic (mT) moves northward across eastern US brings mild, cloudy winters and hot humid summers with hurricanes and thunderstorms

Air Masses Are Classified by Region

small balloon carried observatory that carries a radio transmitter that sends out signals about air pressure, temperature, and humidity

fronts: boundary between two air masses having different temperatures and humidity

warm air overtakes cool air warm air rises brings hot, humid days and precipitation over a large area

Formation of a Warm Front

Cold, dense moves into a region occupied by warm air cold air forces warm air up brings strong storms (squall) with clear days following

Formation of a Cold Front

An active cold front overtakes a warm front The cold front merges with the warm front Light precipitation can fall for several days

Formation of an Occluded Front

does not move

small-area storms formed by the strong upward movement of warm, moist, unstable air always accompanied by lightning, thunder, and usually rain formed from cumulonimbus clouds

Air-mass thunderstorm: form in warm, moist air mass occur in spring and summer- last less than 1 hour single, widely scattered

Frontal thunderstorm: occur in lines along a frontal surface stronger and may last several hours can produce heavy rain and flooding

Lightning: a discharge of electricity from a thundercloud to the ground, or cloud to cloud, or ground to cloud

temperature inside lightning flash can reach 28,000°C at this temperature, air expands explosively-sudden expansion makes thunder!

an intense tropical low- pressure area with sustained winds starting at 75 mph

storm surge: currents formed when hurricanes pile water up along the shore and blow it inland most damaging part of a hurricane

eye: central area of sinking air; 15 to 20 km wide

Winds most violent just outside the eye (eye wall)

Tropical depression: wind speeds up to 38 mph; some circular rotation at surface

Tropical storm: wind speeds from mph; can be named, shows drop in pressure, distinct rotation

Hurricane: wind speeds up to 75 mph

a narrow, funnel-shaped column of spiral winds that extends downward from the cloud base and touches the ground

strongest winds between 360 and 500 km/hr funnel less than 500 m across always travel with a parent thunderstorm at speeds ranging from 40 to 65 km/hr

funnel is a mixture of clouds and dust pressure gets lower in center air flows toward the funnel and cools to dew point- drops form lowering of condensation level due to low pressure causes cloud to funnel Extremely low pressure-when it touches ground, acts like a giant vacuum

Waterspout: tornados over the water- weaker than tornados

Tornados usually occur during spring and summer and most likely occur in late afternoon

Fujita Scale: scale used for categorizing tornados

Meteorologists interpret weather information from: satellites commercial aircraft weather balloons

weather stations around the world Radar: electronic device that transmits radio waves in the form of a beam

Data is collected and put into a central computer at the National Weather Service data includes: winds, temperature, pressure, humidity, clouds, precipitation Makes a computer model (copy of the atmosphere in computer

Maps are made and forecasts are reported to local stations across the country Weather forecasts are issued by the Weather Service at 10 am, 4 pm, 9pm, and 4 am. Forecasts are updated more often during severe weather.

watch: threat of storm conditions within hours warning: due to strike within 24 hours