Transcript Air Masses, Fronts and Predicting Weather

What is the relationship between
air temperature and relative
humidity?
This graph
assumes the
amount of
water in the air
does NOT
change as the
temperature
changes.
Think of air as a container, and we need to
fit a fixed amount of water into the
container.
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When the temperature drops, and water vapor amount
stays the same, the air fills up with water, increasing the
relative humidity.
WARM AIR “container”
FITS MORE WATER =
40% humidity
COLD AIR “container”
FITS LESS WATER=
90% humidity
Air masses and fronts
Aim: Why does the weather change?
Vocabulary:
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Air mass
Source regions
Maritime
Continental
Polar
Tropical
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Fronts
Cold Front
Warm Front
Stationary Front
Occluded Front
Air masses are…
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A volume of air
characterized by
similar pressure,
moisture and
temperature.
Air masses acquire
their properties
from the source
region.
Source regions are where the air mass
comes from
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Maritime – from ocean
Continental – from land
Tropical – warm (L)
Polar – cold (H)
Air Mass Type
Map Symbol
Continental Tropical
cT
Continental Polar
cP
Maritime Polar
mP
Maritime Tropical
mT
Formed over….
Characteristics
Naming air masses
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Air mass names are characterized by their
source regions. Use a 2 letter symbol.
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Maritime tropical (mT) – Warm, humid air
mass from over tropical oceans. Bring
summer showers and thunderstorms,
hurricanes
Maritime polar (mP) – Cool, humid air from
over cold oceans. Bring fog, rain and cool
temperatures, noreasters
Continental Tropical (cT) – Hot, dry air
from over the Southwest and Northern
Mexico
Continental Polar (cP) – Cool or cold, dry
air from over Canada and Alaska
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Warm moist air rises from the equator region,
while cool, dry air sinks from the north. These
air masses collide over the midwest in early
spring causing tornados.
TORNADO
ALLEY
Fronts – where air masses collide
The warmer air rises above the cooler air. It cools, condenses into
clouds and causes precipitation around the front. Fronts signal
changing weather, as a new air mass moves into the area.
There is always precipitation at a
front! Why?
4 kinds of fronts
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Symbols (like flags) point in the direction
the front and air masses are moving
After the front passes, a new air mass
brings new weather conditions
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Cold fronts
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Cooler air mass runs into
a warmer air mass
Warm air is pushed up
rapidly  cumulous
clouds and
thunderstorms, tornados
Passes quickly, shorter
period of rain, heavy
downpours
After  clear skies and
cooler temps (H -cooler,
clearer, drier)
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Warm fronts
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A warmer air mass
runs into cooler air
mass
Warm air rises over
the cold
Passes slowly, clouds
over wider area
Slower moving, drizzly
or steady rain
After  warm and
humid weather
(warmer, wetter,
cloudier)
Stationary Fronts
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Cold and warm air masses
meet but neither move
“standoff”
Water vapor condenses in
the warm air  days of
clouds and precipitation
until one air mass becomes
stronger than the other
and begins to move
Occluded Front
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Warm air mass is
caught between 2
colder air masses
Cold masses
combine and push
the warm up
Makes heavy
clouds, rain or
snow
SUMMARY
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Why does warm air always rise above cool
air?
What always happens at a front?
What type of pressure characterizes a air
behind a cold front?
Warm front?