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•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 lowpressure 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
39-74 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
lowering of
condensation level due
to low pressure causes
cloud to funnel
air flows
toward the
funnel and
cools to dew
point- drops
form
Extremely low
pressure-when it
touches ground,
acts like a giant
vacuum
Waterspout: tornados over the waterweaker 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 24-36 hours
warning: due to strike within 24
hours