Download Student Notes: Air Masses, Fronts and Storms

Notes: Air Masses and Fronts
Air Mass: A huge body of air that has similar temperature, humidity and air pressure at any
given height. (they can spread out millions of kilometers and be up to 10 Km deep)
4 Major Types of Air Masses (classified by temperature & humidity)
Tropical: warm air that forms in the tropics and has low air pressure
Polar: cold air masses that have high air pressure & form at higher latitudes
Maritime: humid air masses that form over oceans
Continental: dry air masses that form over land
How Air Masses Move
Air Masses interact with each other and cause weather changes
Prevailing Westerlies push air masses in the U.S. from west to east
High speed Jet Streams blow air masses west to east
Fronts: the boundary where two air masses meet
Types of Fronts
As air masses and fronts move across the land and oceans, they collide but do
not easily mix together.
The kind of front that develops depends on the characteristics of the air masses
and how they are moving.
Fronts are some of the basic building blocks of weather systems. Fronts occur
where two large air masses crash into each other. Each air mass has a different
temperature. Fronts are caused by winds moving one air mass away from its
birthplace. Fronts are usually associated with rain, snow, or hail.
Thunderstorms, tornados and other severe weather can occur with fronts.
Cold Front
Occurs when a fast moving heavy cold air mass slides
under and pushes a lighter warm air mass upwards.
The rising warm air can hold more water vapor, cools &
condenses. Cumulus clouds form & usually grow into
thunderstorms. Temperatures drop anywhere from 5 to
15 degrees. Winds become gusty and erratic. Rain, snow,
sleet, and hail can occur.
Warm Front
Occurs when a fast moving warm air mass overtakes
and replaces a slow moving cold air mass by sliding
over it.
Clouds form and may be associated with rain, snow,
or sleet depending on the humidity of the warm air.
Temperatures may warm slightly.
Winds are usually gentle with this kind of front.
Stationary Front
Stationary fronts occur when neither warm nor cold
air advances.
The two air masses reach a stalemate. That is what
stationary means - that neither front is moving.
These types of conditions can last for days, producing
nothing but Altocumulus clouds. Temperatures
remain stagnant and winds are gentle to still.
Cyclones and Anticyclones
When air masses collide and a front forms,
the boundary between the fronts sometimes
becomes distorted due to mountains or high
winds. Bends develop along the front and
the air begins to swirl.
Cyclones: A swirling area of low pressure at the surface
Warm air in the center rises and the air pressure decreases at the surface
Winds spiral inward and counterclockwise in the Northern Hemisphere because
of the Coriolis Effect
As warm air rises, it cools and condenses, forming clouds and precipitation.
Associated with BAD WEATHER like Thunderstorms, Hurricanes and Tornadoes
Anticyclone: A swirling area of high pressure at the surface
Cool air moves downward from higher in the troposphere and air pressure
increases at the surface
Winds spiral outward and clockwise from the center and move toward areas of
low pressure
The descending air warms up at the surface
Associated with dry, clear, GOOD WEATHER