Air Masses & Severe Weather
Study Guide
Air Masses
1) What is an air mass?
A huge body of air that has similar temperature, humidity & air pressure is called an air mass.
a) How are they classified?
Classified according to temperature and humidity
b) What is a source region and what types of source regions are there?
A source region is the region form which the air mass originates.
Can be polar, maritime, tropical, or continental
c) know how to classify source regions.
Air Fronts
2) What is a front?
The boundary where the air masses meet becomes a front.
a) How are they classified?
They are classified by which air mass replaces the other
3) Describe a cold front? What is the weather map symbol? Why type of weather does it bring?
A cold front forms when cold air moves underneath warm air, forcing warm air to rise.
They move quickly & bring cold, dry air. Tall storm clouds form. Differences in pressure brings
strong winds ,heavy rain, thunderstorms or snow falls. After the front passes, cold air moves in
& the temperature drops.
4) Describe a warm front? What is the weather map symbol? Why type of weather does it bring?
A warm front forms when warm air moves over cold air. They move slowly & bring warm, humid
air. Many clouds form along the front. First cirrus form high in the sky, then stratus & steady
precipitation follow. After the front passes, warm air moves in & the temperature rises.
5) Describe an occluded front? What is the weather map symbol? Why type of weather does it
bring? An occluded front forms when a warm air mass is caught between 2 two cooler air masses.
The warm air mass is “cut off” from the ground the warm air mass eventually cools & creates
cloudy, rainy or snowy weather.
6) Describe a stationary front? What is the weather map symbol? Why type of weather does it
bring? A stationary front forms when cold & warm air masses meet but neither have enough
force to move the other. They stop moving. It may remain for a short time – there little weather
change. If it stays for a long time – warm-front weather takes over – many days of clouds &
steady precipitation.
Severe Weather
7) Thunder & Lightning
a) What causes thunder storms?
There are two factors for a thunderstorm to occur: warm moist air must be near the surface and
unstable atmosphere. UNSTABLE whenever the surrounding air is colder than the rising air mass.
When rising warm air reaches its dew point, cumulus clouds begin to form In a very unstable
atmosphere, air continues to rise & forms dark cumulonimbus clouds that reach heights more
than 15 km. Electric charges may build, producing lightning
b) What causes lightning? Lightning is produced in thunderstorms when liquid and ice particles
above the freezing level collide, and build up large electrical fields in the clouds. Once these
electric fields become large enough, a spark occurs between them.
i) Which comes first, thunder or lightning? They occur at the same time.
8) Tornadoes
a) What causes tornadoes? Air moves in 2 directions, causing the air in the middle to spin. The
air turns vertical by updrafts. The tornado is classified as a tornado once the funnel cloud
touches the ground.
b) What is it called when it doesn’t touch the ground? A funnel cloud
c) How are they measured? Which is the deadliest? Fujita scale, based on wind speed and
destructiveness. F5 is the deadliest.
d) What are they called when they occur over water? Waterspouts
e) What is the area called when they occur most often in the United States?
Tornado alley
Hurricanes
9) What is a hurricane? Large rotating tropical weather systems that have wind speeds of at least 75
mph
a) What are they called in the Pacific Ocean? Indian Ocean? Pacific: Typhoon
Indian ocean: Cyclone
10) What does a hurricane need to grow? Warm water
a) Why doesn’t a hurricane form over land? It needs the strength of the warm water to build
strength
11) How are they measured?
Measured on the Saffir Simpson scale. Start as tropical depression, then tropical storm then
become a hurricane 1-5, 5 being the most severe.
a) When are they considered a tropical depression? Tropical Storm?
When just forming it is a tropical depression, as it builds up strength and wind speed it
becomes a tropical storm.
b) What is the center of a hurricane called? What is the weather like there?
An eye, calm weather there.
Cyclones & Anticyclones
12) Cyclones surround which type of pressure? Which direction do they spin? What type of weather
do they bring?
Cyclones are areas where air masses come together & rise. It is an area in the atmosphere that has
lower pressure than the surrounding areas & has winds that spiral towards the center Referred to as
cyclone. Rotate counterclockwise. Clouds, winds & precipitation are associated with lows
13) Anticyclones surround which type of pressure? Which direction do they spin? What type of
weather do they bring?
Anti-cyclones are areas where air masses move apart & sinks. It is an area in the atmosphere that
has higher pressure than the surrounding areas & has winds that spiral outwards. Referred to as
highs. Rotate clockwise. Dry, clear weather is associated with highs