Download Air Masses and Severe Weather

Air Masses,
Weather Fronts
and Severe
Weather
Air Mass
Large volume of air with similar
temperature and humidity that
can cover entire continents or
oceans
Several types that each have
specific characteristics
Types of Air Masses
mP- maritime Polar: cold air masses
that form over the oceans near the
poles
Cold and Moist Air
cP- continental Polar: cold air masses
that form over land near the poles
Cold and Dry Air
Types of Air Masses Cont’d
mT- maritime Tropical: warm air mass
that is formed over the oceans near the
equator
Warm and Moist Air
cT- continental Tropical: warm air mass
that is formed over land near the
equator
Warm and Dry Air
Effects of Physical
Features
Physical features of the Earth,
such as, lakes, valleys, and
mountains can affect the
movement of air masses
Atmospheric Lifting Type #2
Orographic Lifting
An air mass is pushed
upward over an
obstacle, such as a
mountain range.
Atmospheric Lifting of Air
Masses over a Mountain
As the air mass is pushed
over the mountain, the air
mass will lose moisture in
the form of clouds, rain, or
snow
Atmospheric Lifting Type #2
Atmospheric Lifting Type #2
Atmospheric Lifting
The clouds
dump their load
of rain on the
windward slope
The down slope
(leeward) air
will be dry =
rain shadow
Rain shadow-
Rain shadow
Western
Kansas is so
dry only
certain short
grasses can
grow; not
enough rain
for trees
Rain Shadow; Big Hatchet Mt, New
Mexico. Notice how dry the land is
Weather Fronts
This is the boundary between two air
masses with different temperatures.
Weather fronts are the site where most
weather takes place.
There are four types of weather fronts.
Cold Front
When a cold air mass
moves into a warm air
mass.
Cold, denser air forces the
warm air up where it cools
and condenses, forming
clouds
Cold Front:
Warm air is
quickly pushed
upward,
cooling,
condensing
moisture into
cumulus or
cumulonimbus
clouds
Cold Front
Notice how
steep the angle
is between the
two air masses
Typically brings
sudden, heavy
rains and
storms
Cumulonimbus Clouds of a Cold Front
Cumulonimbus: Lake Superior
Warm Front
WARM FRONT:
when a warm
air mass moves
into a
colder,denser
air mass.
Warm air rides
up and over
the colder air
Warm front
Warm Front
Notice the angle of slope between the
two air masses.
Warm Front
The weather
during a WARM
FRONT starts
with cirrus
clouds about
24-48 hours
before the rain
begins
Cirrus clouds
are “at the front
of the front”
Warm Front
As the warm
front approaches,
heavier clouds
form over the
cold air
These are stratus
clouds.
Warm Front
Warm fronts
bring light
rain or snow
that can last
for several
hours or days
Stationary Fronts
Two air masses
come together but
neither one is
pushed out
Can last several
days
Stratus and
nimbostratus clouds
produce steady rain
Stationary Front
Occluded Front
A mass of warm air
gets trapped
between two
masses of cold air
Warm air gets
squeezed out
Produces
stratocumulus
clouds and heavy
rain or snow
Severe
Weather
Thunderstorms
Cold Fronts
Begins with humid air rising,
cooling, and condensing into a
single cumulus cloud.
Cloud builds as they are
“fueled” by warm, moist air
from below.
Thunderstorms
The droplets
of water
grow larger
until they
are so big
that they fall
as rain.
Cumulonimbus clouds: L Superior
Thunderstorms (con’t)
Lightning may be
associated with T.storms
Hits Earth 100 times per
second
Over 200 people in the US
die each year from
lightning.
Lightning
Lightning is the cause of
thunder
Returns nitrogen to the soil
Frequently causes forest fires
Lightning Formation
During
thunderstorms
strong updrafts
cause molecules to
bump together and
their charges to
separate
Negative charges
concentrate at the
base of the clouds
Lightning Formation
The ground has lost
electrons, giving it a
positive (+) charge
Opposites attract:
The (-) from the
cloud base is “pulled”
to the (+)
First downward
movement of (-) is
called a leader
Lightning Formation
When the (-) and
(+) touch, they
create a
conductive path to
the ground.
The other (-) rush
down this path =
lightning
Lightning on L.Superior
Lightning on L.Michigan
Lightning strike
Tornadoes
A funnel shaped cloud that extends
downward from a cumulonimbus cloud.
Called a tornado only once it hits the
ground.
Winds inside travel at up to 800km per
hour in counterclockwise direction.
Tornado: February 25, 2008
Hurricanes
Caused when a warm, vertical wind mixes
with a storm and causes the storm to turn
inward and begin spin.
Wind speeds of up to 180miles per hour.
Hurricanes grow as more moist air rises into
it.
Strong winds rotate around a calm, low
pressure zone in the middle, which is the eye
of the storm.
Hurricane Mitch
Requirements
Tropical Depressionwind speeds <45 mph
Tropical Storm
Wind speeds >45 mph but <74 mph
Hurricane
Wind speeds >74 mph