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•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 frontthe 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
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
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
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: NOAA
Check out this website!
http://www.weather.com/web/newscenter/specialreports/
hurricanes/inside/elements.html
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
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: NOAA
The coasts of
Louisiana,
Mississippi,
Alabama and
part of Florida,
seen from space
on October 15,
2001. Original
photo from
NASA
A gigantic, dangerous
storm, Hurricane
Katrina takes aim at
New Orleans and the
Mississippi coast.
Photo: NASA
Meteorologists interpret weather
information from:
satellites
commercial
aircraft
weather balloons
Eastern U.S.-Infrared Satellite
Ophelia
11:45 am 9/14/05
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 24-36 hours
warning: due to strike within 24
hours