Download Air Masses and Fronts

Air Masses and Fronts
Mr. Bombick
7th Grade Science
Types of Air Masses
• There are four major types of air
masses that affect our weather.
• These four major types of air masses
are maritime tropical, continental
tropical, maritime polar, and continental
polar.
• Tropical air masses are warm while polar
air masses are cold.
• Maritime air masses form over oceans
and continental air masses form over
land.
Types of Air Masses (cont.)
• Maritime tropical air masses bring warm and
humid air first to Southeastern and
Southwestern parts of the US. In summer,
rain and thunderstorms can result and in
winter, heavy rain or snow may result.
• Maritime polar air masses bring cold and
humid air mainly to the West Coast. They
may result in fog and rain in summer and snow
in the winter.
Type of Air Masses (cont.)
• Continental tropical air masses form over dry
areas of the Southwest and northern Mexico.
These air masses may bring hot and dry
conditions to the lower Southern plains.
• Continental polar air masses form over central
and northern Canada and Alaska. These air
masses can bring clear, cold, and dry air to
much of the US in the winter. During the
summer, these air masses bring colder air to
the US and storms may occur if this air mass
collides with a maritime tropical air mass.
How Air Masses Move
• Prevailing westerlies (major wind belt
over the continental US) push air
masses from west to east.
• Jet streams help direct air masses from
west to east.
• Fronts are the boundaries of where
large air masses meet or collide. Fronts
are often areas of changing weather.
Warm air rises
Cold air sinks
Warm air can contain more
water than cold air
Types of Fronts
• Cold fronts develop when a fast-moving
cold air mass overtakes a warm air mass.
There is usually significant cloud
formation and heavy rain or snow may
fall if the warm air contains a lot of
water vapor. Sudden weather changes
are possible including thunderstorms.
After a cold front passes, colder and
drier air moves in, often with clear
skies.
Types of Fronts (cont.)
• Warm fronts result when a fast-moving
warm air mass overtakes a slower
moving cold air mass. Light rain or snow
may fall along the front which may
remain for several days. After a warm
front passes, the weather may be
warmer and more humid.
Types of Fronts (cont.)
• A stationary front is where a warm and
cold front meet but, neither can move
the other. There can be precipitation
and cloud formation at the boundary
between the two fronts. A stationary
front can stall which may result in many
days of clouds and precipitation.
Types of Fronts (cont.)
• An occluded front is a complex weather
pattern where a warm front becomes
trapped between two cold fronts.
There may be precipitation associated
with this front if the warm air starts to
cool and water vapor condenses.