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WEATHER PATTERNS
QUESTION
What are the major types of air masses in North
America and how do they move?
AIR MASS
Large body of air that has uniform temperature,
pressure, and humidity
Air masses are classified by temperature and moistureMaritime-those formed over water
Continental-those formed over land
Tropical-those that are warm
Polar- those that are cold
HIGH-PRESSURE SYSTEM
Large body of circulating air with high pressure at its
center and lower pressure outside the system; brings
sunshine and good weather
LOW-PRESSURE SYSTEM
Large body of circulating air with low pressure at its
center and higher pressure outside the system;
brings clouds and precipitation
IN CONTINENTAL THE US
Air masses are commonly moved by prevailing
westerlies and jet streams. Colliding air masses can
form different types of fronts
Cold Fronts: cold air moves under warm air forcing the
warm air upwards
Warm Front: move slowly and brings warm, humid air
IN CONTINENTAL THE US
Stationary Front: forms when a cold mass meets a
warm mass but neither have enough force to move
one another
Occluded Front: warm air mass is caught between
two cold air masses
WHAT IS A STORM?
Violent disturbance in the atmosphere called severe weather
 Thunderstorms: small storm accompanied by thunder and lightning formed from large cumulonimbus
clouds
 Tornado: rapidly, whirling, funnel-shaped cloud that reaches down from a storm cloud and touches the
Earth’s surface formed when a thunderstorm updrafts begin to rotate
 Hurricane: intense tropical storm with winds exceeding 119 km/hr formed over warm ocean water as a
low-pressure area
 Blizzard: violent winter storm characterized by freezing temperatures, strong winds and blowing snow
WEATHER MAP CODES