Download Air Masses and Fronts

Air Masses and Fronts
What is an Air Mass?
•  Air masses are large bodies of air which have
similar temperature and moisture characteristics.
•  Air masses form when air stays over a region
(called the source region) for several days.
•  Air masses that form over water will be moist.
•  Air masses that form over land will be dry.
Latitude determines temperature
Moisture determined by whether it forms
over oceans or continents
c continental = dry
A=
Arctic
P=
Polar
T=
tropic
m marine = moist
Continental Polar does not move west
Fronts – boundary that separates
2 air masses with different temperatures
Cold Front
a. short-lived thunderstorms
b. move faster than warm fronts
Warm Front – longer, steady
precipitation
Stationary Front
•  A stationary front occurs when the air masses on
either side of the front are not moving toward each
other.
OCCLUDED FRONT
Warm air mass gets caught between 2
colder air masses and is forced upward
Occluded Front
Winds spiral clockwise out of the High
and counterclockwise into the Low
Fronts are low pressure – lousy weather
After the front passes – happy weather
Remember this!
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Warm air = less dense
Warm air rises!
Cold air = more dense
Cold air sinks!
Weather Changes after Fronts Pass
•  2 TOTALLY different air masses so a
change in weather
•  Temperature changes
•  Wind direction changes
•  Wind velocity changes
•  Dew Point changes
•  Barometer falls when front approaches and
rises after it passes
BRRR!
WINDS FLOW COUNTERCLOCKWISE IN TO
THE LOW PRESSURE SYSTEM – RISING AIR
WINDS FLOW CLOCKWISE OUT OF THE HIGH
PRESSURE SYSTEM – SINKING AIR
Hurricanes – counterclockwise low
pressure systems (lousy weather)
Weather in a High
•  Clockwise
Rotation
•  Bright, Clear
•  Happy Weather
LAKE EFFECT - SNOW
Box 9.2
Thunderstorm Facts
•  At any given time there are an estimated 2000
thunderstorms in progress, mostly in tropical and subtropical latitudes. - About
45,000 thunderstorms take place each day
•  Annually, The U.S. experiences about 100,000
thunderstorms.
•  About 16 million thunderstorms occur annually
around the world!
•  The lightning from these storms strikes Earth
about 100 times each second
Lightning
•  Within the thunderstorm
clouds, rising and falling air
causes turbulence which
results in a build up of a
static charge. The negative
charges concentrate in the
base of the cloud.
•  This first, invisible stroke is
called a stepped leader.
•  As soon as the negative and
positive parts of the stepped
leader connect there is a
conductive path from the
cloud to the ground and the
negative charges rush down
it causing the visible stroke.
Tornadoes
•  Area of quickly rotating air
associated with a
thunderstorm
•  Some contain winds of over
300 miles per hour
•  They can be as small as a
hundred yards wide or
larger than a mile wide