a large body of air that has the same temperature and humidity throughout classified according to where they originate as it moves, the characteristics of an air mass change and so does the weather in the area over which the air mass moves.

Air Masses Are Classified by Region

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

View satellite movies of air masses moving across North America.

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

forms when warm air moves into an area formerly covered by cooler air brings hot, humid days and precipitation over a large area

forms when cold, dense air moves into a region occupied by warmer air brings strong storms (squall) with clear days following

Compare and contrast warm and cold fronts.

two cold masses sandwich a warm mass brings strong winds and heavy rains

the flow of air on either side of the front is neither toward the cold air mass nor toward the warm air mass, but almost parallel to the line of the front- the surface position of the front does not move

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

Observe an animation of a thunderstorm.

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!

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

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

Eye of hurricane Floyd

Winds most violent just outside the eye

Aug. 28, 2005: Katrina's eyewall was seen from a hurricane-hunter plane. Photo: NOAANOAA

hurricanes/inside/elements.html Check out this website!

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

Movement of Air in a Hurricane

There are sometimes gaps in between these bands where no rain is found. In fact, if one were to travel between the outer edge of the hurricane to its center, one would normally progress from light rain to dry back to slightly more intense rain again over and over with each period of rainfall being more intense and lasting longer until reaching the eye. Upon exiting the eye and moving towards the edge of the hurricane, one would see the same events as they did going in, but in opposite order.

A schematic of this banding feature can be seen in the diagram above. The thunderstorms are now organized into regions of rising and sinking air. Most of the air is rising, but there is a small amount found in between the thunderstorms that is sinking.

Satellite image of Hurricane Katrina on Aug. 28, 2005, when the storm was a Category Five hurricane. Hurricanes don't get much stronger than this. Photo: NOAANOAA

The coasts of Louisiana, Mississippi, Alabama and part of Florida, seen from space on October 15, Original photo from NASA NASA

A gigantic, dangerous storm, Hurricane Katrina takes aim at New Orleans and the Mississippi coast. Photo: NASANASA

Meteorologists interpret weather information from: satellites commercial aircraft weather balloons

Eastern U.S.-Infrared Satellite 11:45 am 9/14/05 Ophelia

Eastern U.S.- Visible Satellite

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.

Interactive Weather Page

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