AIR MASSES
• A large body of air (thousands
of miles)
• Changes in weather are caused
by movements of air masses
• As an air mass moves away,
temp & humidity change.
Classification
•Air masses are named from
the area where they come
from.
• Classified according to :
temperature & moisture
content.
• Tropical- HOT air mass
formed in tropics
• Polar- COLD air mass formed
near poles
• Maritime- air mass formed
over oceans, WET
• Continental- air mass formed
over land, DRY
TYPES OF AIR MASSES
1. MARITIME TROPICAL
2. MARITIME POLAR
3. CONTINENTAL POLAR
4. CONTINENTAL
TROPICAL
Warm, humid air mass formed
over ocean near equator.
Summer = hot humid weather
Winter = heavy rain/snowfall
Cool, humid air masses formed
over ocean near poles
Summer = cool temps, fog, rain
Winter = snow, cold temps
• Hot, dry air masses formed
mostly in the summer over dry
lands of SW & N Mexico.
Large, cold air mass formed
over land in Canada & Alaska.
Winter- extremely cold, dry air.
Summer- cold, dry air temps
• Prevailing Westerlies push air
masses west to east.
• Jet Stream- blow west to east
• Fronts- boundaries between air
masses, changeable weather &
storms develop along fronts.
• Colliding air masses can form
4 types of fronts:
1. Cold fronts 2. Warm fronts
3. Stationary fronts
4. Occluded fronts
• forms when a cold air mass
meets & pushes under a warm
air mass.
• Warm air cools, clouds form,
& heavy rain. (thunderstorms).
• cool weather
• Forms when a warm air mass
moves over a cold air mass.
• Rain showers then hot, humid
weather.
• Warm air mass meets a cold
air mass & no movement
occurs. Produces rain &
clouds.
• When a warm air mass is
caught between 2 colder air
masses. Warm air cut off.
• Produces clouds, rain/snow.
• A center of low air pressure,
winds spiral inward.
• As air rises in a cyclone, the
air cools forming clouds &
precipitation.
•High pressure areas of dry
air where winds spiral
outward. (clockwise)
•Descending air in an
anticyclone causes dry,
clear weather.
STORM
•A violent disturbance in
the atmosphere
• A small storm often
accompanied with heavy
precipitation & thunder &
lightning.
• Form in large cumulonimbus
clouds called thunderheads.
• On hot, humid days, warm air
rises rapidly, & cools forming
cumulonimbus clouds.
• This movement of air creates
updraft & downdraft winds.
Areas of (+)/(-) charges build up
in storm clouds. It is a sudden
discharge of electricity
between 2 clouds or the cloud
and the ground. Electric
energy is released.
Light travels faster than sound.
Lightning heats air. Heated air
expands rapidly which results
in sound waves (thunder).
T-Storm Damage
• Heavy rains which can lead
to floods.
• Lightning, Hail, & winds
can cause damage.
• Whirling, funnel shaped cloud
that reaches down from a
storm cloud to touch earth’s
surface.
• Warmth & Moisture feed it
• Season: late spring/early
summer
• Warm, humid air meets cold, dry
air. A squall line of thunderstorms
develop which can develop into a
tornado.
• Warm air rises rapidly & begins to
rotate. The cloud will then start to
descend to earth in a funnel.
• Tornado Alley- Mid-West US
• This is where the conditions
are the best- warm, humid air
from Mexico mixes with cold,
dry air from Canada.
• Tornadoes occur most frequently
in the US
• Damage comes from strong winds
& flying debris.
• Tornadoes are ranked on the
Fujita Scale (by the amount of
damage they cause.)
• F0 light damage to F5 extreme
damage.
• F4 F5 tornadoes account for
only 1% of all tornadoes.
• A tropical cyclone that has
winds of 119kmh or higher.
• Forms in the Atlantic, Pacific,
& Indian Oceans. In western
Pacific- typhoons.
HURRICANE FORMATION
• It begins over warm ocean water
as a low-pressure area (tropical
disturbance).
• It grows from a disturbance to a
tropical storm and maybe to a
hurricane.
• It draws energy from warm,
humid air at ocean’s surface.
• Warm air rises to form clouds,
more air is drawn into the
system.
• Storms bands, high winds, &
heavy rains spiral around a
center.
• Cool, dry air sinks into the
center (eye) of the hurricane.
• Hurricanes last longer than
other storms- usually a week
or longer.
• Year round, most precipitation
begins in the clouds as snow.
• Cold, dry air moves across
warmer water picking up water
vapor & heat from the water.
Once the air reaches the other
side of the lake, air condenses
& falls as snow.
• In New York, Buffalo &
Rochester are 2 of the
snowiest cities in the US
because of Lake-Effect
Snow.
Snowstorm Safety
• Find shelter from the wind.
• It can be dangerous because
high winds/snow limit your
vision so you can get lost
easily & you can lose a lot of
body heat out in the cold.
Meteorologists
• Scientists who study the causes
of weather & try to predict it.
• Meteorologists use maps,
charts, & computers to analyze
weather & prepare weather
forecasts.
• Lines joining places that have the same temps.
• Lines joining areas with the same air pressure.
TECHNOLOGY
• Has improved the accuracy of
weather forecasts.
• Weather balloons carry
instruments into the
troposphere & stratosphere to
measure temp., air pressure, &
humidity.
• Weather Satellites- orbit earth
in the thermosphere, cameras
make images of the earth’s
surface, clouds, & storms
which get sent to
meteorologists to analyze.
• Computer Forecasts- gathers
weather data from a large area
then the computer works
through thousands of
calculations using equations
from weather models to make
forecasts for 12, 24, & 36
hours. Each one builds on the
previous forecasts.