Air mass

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Weather Notes
Weather is caused by the movement and interaction of air masses
Air mass – a large body of air that has properties similar to the parts of
Earth’s surface over which it develops
 Earth air mass is described with a Temperature and Moisture
(must have one of each)
o Temperature
 Warm (tropical)
 Cold (polar)
o Moisture
 Moist (maritime)
 Dry (continental)
 Example of an air mass: Maritime/Polar, Continental/Tropical
Pressure Systems
 High pressure system:
o High pressure does not allow air to rise and form clouds
o Gives Fair/nice, “good” weather
o Moves clockwise (in northern hemisphere)
o HINTS:
 giving a “HIGH 5” = GOOD
 “thumbs up/high” = GOOD
 HIGH (4 letters), GOOD (4 letters)
 Low pressure system
o Low pressure allows warm air to rise, which forms
clouds
o Gives cloudy, “bad” weather, usually with precipitation
o Moves counter-clockwise (in northern hemisphere)
o HINTS:
 “thumbs down” = bad
 LOW (3 letters) = BAD (3 letters)
Fronts - a boundary that forms between 2 different air masses
 Usually cloudy and stormy at a front boundary
 4 types of fronts
o Cold Front, Warm Front, Stationary Front, Occluded
Front
Front
Description of Front
Cold
Front
-
-
cold air rapidly pushes up warm air
can result in rain, large thunderstorms, and possible
tornadoes (“drama queens”)
leaves a colder air mass over area, temps may drop
Warm
Front
-
-
warm air moves over a receding (leaving) colder air
mass
results in several hours, or days of precipitation
Weather Map
Symbol
Front
Description of Front
Stationary
Front
-
-
warm air and cold air meet
little or no movement between air masses
results in light precipitation and wind for several
days
Occluded
Front
-
-
involves 3 air masses of different temperatures
2 air masses “squeeze” and force warmest air mass
upward
causes precipitation
Weather Map
Symbol
Severe Storms
 Thunderstorms/Hail
o Usually occurs along cold fronts
o Heavy rain, lighting, thunder, heavy winds
o Hail may form
 Hail – ice crystals that form and grow larger through
updrafts and down drafts in thunder clouds
 Tornadoes
o Violently rotating columns of air that make contact with the
ground
o Formed during severe thunderstorms
o Strong winds move in many directions at many speeds
causing a rotating column parallel with the ground. The
updraft of the thunderstorm causes the column to tilt
vertically (up and down). When the column hits the ground,
it is called a tornado.
o Tornado alley – a group of states in the midwest prone to
tornadoes due to the severity of thunderstorms and flat
land
 Hurricanes
o most powerful severe storm
o large, swirling, low pressure system that forms over warm
water
o turns heat energy from the ocean into wind
 Blizzards
o Severe snow storms
o Strong winds with low visibility due to falling snow
o Low temperatures
o Must continue for at least three hours
 Severe Weather Safety
o National Weather Service will announce watches and
warnings through various tools (i.e. radio, computer
websites, twitter, facebook, text messaging, television)
o Seek shelter indoors when possible
o Secure loose items outside
o Evacuate if requested by government/National Weather
Service
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