Transcript Weather Patterns

Weather Patterns
Weather Changes
• Because of the
movement of air
and moisture in
the atmosphere
weather
constantly
changes.
Air Masses
• Air Mass; A
large body of air
that has the
properties similar
to the part of the
Earth’s surface
over which it
develops.
Air Masses
Air Masses
• When you
observe a
change in the
weather from
one day to the
next, it is due to
the movement of
air masses.
Atmospheric Pressure
• Remember winds
blow from areas of
high pressure to
areas of low pressure.
• Variation in
atmospheric pressure
affects the weather.
Low Pressure
• Low pressure
systems at
Earth’s surface
are regions of
rising air. Clouds
form when air is
lifted and cooled.
Low Pressure
• Areas of low
pressure
usually have
cloudy
weather.
High Pressure
• Air sinks in high
pressure air
masses. This
sinking makes it
difficult for air to
rise and clouds
to form.
High Pressure
• High
pressure
usually
means good
weather.
Fronts
•
•
Front: A boundary between two air
masses of different density, moisture, or
temperature.
Four types of fronts:
1.
2.
3.
4.
Cold
Warm
Occluded
Stationary
Cold Front
• A cold front is shown
on a map as a blue
line with triangles.
• A cold front occurs
when colder air
advances toward
warm air.
• The cold air wedges
under the warm air
like a plow.
Cold Front
• As the warm air is lifted, it
cools and water vapor
condenses, forming
clouds.
• When the temperature
difference between the
cold and warm air is
large, thunderstorms and
even tornadoes may
form.
Warm Front
• Warm fronts occur
when lighter,
warmer air
advances over
heavier, colder air.
• A warm front is
shown on weather
maps as a red line
with red
semicircles.
Warm Front
• At the contact of
the front the
temperatures are
warm, winds are
light and drizzle
may occur.
Occluded Front
• Occluded front
involves three air
masses.
– Colder air
– Cool air
– Warm air
Occluded Front
• Occluded front forms
when a cold air mass
moves toward cool air
with warm air in
between. The colder
air forces the warm
air upward, closing off
the warm air from the
ground.
• Long steady rains can
result.
Stationary Front
• A stationary front
occurs when a
boundary between air
masses stops
advancing. A
stationary front may
remain in place for
several days
producing light wind
and precipitation.
Stationary Front
• A stationary front is
represented by
alternating red
semicircles and blue
triangles. The blue
triangles point toward
the warm air and the
red semicircles point
toward the cool air.
Thunderstorms
• Thunderstorms occur
in warm, moist air
masses along fronts.
• Warm moist air can
be forced upward
where is cools and
condensation occurs,
forming
cumulonimbus
clouds.
Thunderstorms
• Condensation creates water droplets or
ice crystals.
• These small droplets collide to form larger
droplets.
• As the droplets fall toward Earth they
continue to collide and grow larger.
• The raindrops cool air around them.
• This cool dense air then sinks and spreads
toward the Earth.
Thunderstorms
• The sinking, rain
cooled air and
strong updrafts
of warmer air
cause strong
winds.
Thunderstorms
Thunderstorms
• Thunderstorms may
stall over a region,
causing rain or hail to
fall heavily for a
period of time.
Flooding may then
occur.
• Strong winds or hail
can also occur.
Lightning
• What
causes
lightning?
Lightning
• Inside a storm cloud,
warm air is lifted
rapidly as cooler air
sinks.
• This movement of air
can cause different
parts of a cloud to
become oppositely
charged.
Lightning
• When current flows
between regions of
opposite electrical
charge, lightning
flashes.
• Lightning can occur
within a cloud,
between clouds, or
between a cloud and
the ground.
Thunder
• What causes
thunder?
Thunder
• Thunder results from the rapid heating of
air around a bolt of lightning.
• This extreme heat causes air around the
lightning to expand rapidly.
• The heated air then cools quickly and
contracts.
• The rapid movement of the molecules
forms sound waves heard as thunder.
Tornadoes
• Tornado: A
violently
rotating column
of air in contact
with the
ground.
Tornadoes
• In severe
thunderstorms,
wind at different
heights blows in
different
directions and at
different speeds.
Tornado Formation
• This difference in
wind speed and
direction, called
wind shear,
creates a
rotating column
parallel to the
ground.
Tornado Formation
• A thunderstorm’s
updraft can tilt the
rotating column
upward into the
thunderstorm creating
funnel cloud.
Tornadoes
• If the funnel
touches the
ground, it is
called a
tornado.
Tornadoes
• Tornadoes
can be
severely
destructive.
Tornadoes
• What do you think
causes the most
injuries and deaths
during a tornado?
Tornadoes
•What is the
most powerful
storm?
Hurricanes
Hurricanes
• A hurricane turns
heat energy from
the ocean into
wind. A storm must
have winds of at
least 119km or
74mph to be called
a hurricane.
Hurricanes
• Similar storms in the Pacific are called typhoons
and cyclones in the Indian Ocean.
Hurricanes
• Where do our
hurricanes
usually
develop?
Hurricanes
• The strongest hurricanes usually
develop as a low pressure system
west of Africa.
• Steered by surface winds, these
storms move west, gaining strength
from the heat and moisture of the
warm ocean water.
Hurricanes
•What aspect of a
hurricane
causes the most
damage?
Storm Surge
Storm Surge
• Storm surge is water that is pushed
toward the shore by the force of the
winds swirling around the storm. This
advancing surge combines with the
normal tides to create the hurricane
storm tide, which can increase the
mean water level 15 feet or more. In
addition, wind driven waves are
superimposed on the storm tide.
Hurricanes
• What can reduce the
energy of a hurricane?
Hurricanes
1. Landfall
2. Cool ocean waters
3. Wind shear
Blizzards
• Blizzard: A winter
storm with winds at
56k/h, the
temperature low, the
visibility is less than
400 m, in falling or
blowing snow and
these conditions must
persist for at least
three hours.
Blizzards
Snowfall