Transcript A Cold Front…

Why do we have weather?
1. The sun is what causes us to have weather.
As solar energy reaches the Earth, the air
masses at the equator heat up more than at
the poles.
2. Warm air and water at the equator travel
toward the poles
3. Cold air and water at the poles travel toward
equator
4. It is the atmosphere's struggle for
temperature balance that brings us our
changing weather.
The Atmosphere’s Struggle
An air mass is a large dome
of air which has similar
temperature and moisture
characteristics.
What is a storm?
Storms are very
simple to understand
Areas in our
atmosphere that have
low air-pressure and
winds that spiral in
toward the center form
the many different
types of storms.
Types of storms
Extratropical storms:
 Form outside the tropics
 Center of storm is colder than
the surrounding air
 Has fronts
 Strongest winds in the upper
atmosphere
 Causes tornadoes,
Tropical storms:
thunderstorms
Form over a tropical ocean
Center of storm is warmer
than the surrounding air
Has no fronts
Strongest winds are near
the Earth's surface
Causes hurricanes, typhoons
What is a Front?
When 2 air masses with different properties meet and
do not combine together, the area between them is
called a front.
There are 4 types of fronts:
Cold Front
Warm Front
Occluded Front
Stationary Front
What is a cold front?
A Cold Front…
forms when warm air moves up, and cold air rushes in
beneath it.
the air masses crash together and the cold front goes
down and the warm front goes up.
A Warm Front forms…
…when a
mass of warm
air overtakes a
cold air mass
and moves
over it.
Steady rain and light showers usually are
associated with Warm Fronts.
What do they mean by Occluded?
To occlude means to block or hide someone or something.
An Occluded Front…
o forms when a Cold Front overtakes a Warm Front.
o produces less extreme weather such as rain and wind
The Tale of the Fighting Fronts
Since a cold front is the boundary between cool and warm air
when the cool air is replacing the warm air, and a warm front is
the boundary when the warm air is winning the battle in the
sky…what happens when neither one is winning?
This known as a stationary front. Stationary fronts often
bring several days of cloudy, wet weather that can last a week
or more
A Tornado is…
1. A violent whirling wind, extending from
the base of a thunderstorm cloud to the
ground.
2. A tornado over a lake or ocean is called a
waterspout.
Tornadoes
The most destructive winds – speeds of up to
310 mph -- faster than Indy 500 race cars
Winds act like a vacuum -- sucks up air that
crashes together and spins
Before…
…..After
Microbursts
Very concentrated bursts of air that
blast down from thunderstorms.
 In a Microburst, air falls at
speeds of 90 mph (in normal
storms air falls about 10 mph)
The name "monsoon" comes from an Arabic word
which means "season" or "wind-shift".
Arizona Monsoons occur during the late summer
months.
In the winter, wind flows to Arizona from California
and Nevada.
In the summer, the winds shift bringing moisture
from the Pacific Ocean and the Gulf of Mexico.
This change, together with daytime heating,
brings Arizona monsoons.
How a Monsoon forms
Are Monsoons only in Arizona?
No, the most well known
monsoons are those
which affect India and
Southeast Asia.
The summer monsoon
blows southwest across
the Indian Ocean and is
extremely wet.
The winter monsoon
blows northeasterly and
is generally dry.
Dust Devils
Look like mini tornadoes,
but tornadoes form high
in the sky, devils form on
the ground
Happens when ground
gets really hot and heats
up air;air rises fast and
bangs together, spinning
around
Sucks up dust and dirt
Fastest devils spin about
40 mph
Hurricanes are actually a kind of Tropical Storms
Tropical storms are large rotating storm systems that form in the Atlantic,
Indian, and Pacific oceans.
 In the Atlantic and eastern
Pacific they are called hurricanes.
 In the western Pacific they are
known as typhoons, which means
“great winds” in Chinese.
 Those in the Indian Ocean are
called cyclones, or by Australians,
willy-willies.
 No matter which term is used, they
all describe this phenomenon
How a hurricane begins
Great Hurricane of 1938
 The eye was about 50 miles across
and the hurricane was about 500 miles
wide.
 Winds gusting over 180 mph and
waves between 30 and 50 feet pounded
the coastline with millions of tons of sea
water.
 Entire homes and families were swept
into the sea.
 Most people did not even realize that
a hurricane was upon them even as the
waters began flooding their coastal
homes.
 Providence, Rhode Island was 20 feet
underwater while Westhampton Beach,
a mile inland, was under 8 feet of water!
Types of Precipitation
Rain - Liquid drops of water which fall from the clouds
Snow - Falling ice formed when water vapor turns into ice.
Sleet - Drops of rain that freeze into ice as they fall.
Hail - Falling ice balls formed during thunderstorms.
Snowstorms
Rainstorms and Snowstorms
Rainstorms and Snowstorms are produced
when two different fronts collide. (A warm
hitting a cold or a cold hitting a warm.)
Major effects could be huge blizzards, ice
storms and heavy rainstorms also known
as Monsoons.
Blizzards
In the winter, when a warm front moves
in and meets a cold front, clouds
develop and heavy snowfall occurs.
There are ice crystals in clouds. When
many tiny crystals build up, they fall to
the Earth as snow.
A blizzard is a name for a violent,
bitterly cold wind with blowing snow
whipped up from the ground.
What makes a snowstorm into a
blizzard?
A snowstorm becomes a
blizzard when you can’t
see very far ahead of you
for three or more hours.
Winds of 35 mph or more
along with lots of falling
and/or blowing snow
Temperature of less than
20 degrees
Thunderstorms
 Thunderstorms are produced when cold
fronts move in and meet warm fronts.
 Thunderstorms are heavy rainstorms
accompanied by thunder and lightning.
Thunder and Lightning
Thunder is created when lightning heats up the air around
it and causes it to expand rapidly.
Since light travels very fast, you see lightning as it
happens.
Sound travels much slower than light and takes much
longer to get to you. You hear the thunder after you see the
lightning.
It takes thunder 5 seconds to travel one mile. After you see
a flash of lightning, start counting seconds until you hear
the thunder. Divide the number of seconds by 5. This is the
number of miles away the lightning is.
Hailstorms and Hailstones
Hail forms when strong
currents of rising air carry
rain from thunderstorms
upwards where it freezes
into ice.
Hail often melts before it
reaches the ground, but in
sometimes ice chunks the
size of softballs pound the
countryside
Floods
A flood occurs when
a body of water
rises and overflows
onto normally dry
land.
Coastal Flooding
Caused by high, windgenerated water waves,
high tides, erosion of
coastal areas, and
tsunamis (underwater
earthquakes).
Coastal flooding is a
big concern because, in
many people live along
coastlines all over the
world.
River Flooding
When it rains and snow
melts, the soil can only
absorb water a certain
amount of water in a
short period of time.
The longer it rains, the
more likely it is that
rainwater will build up
on the ground as runoff
and overflow lakes,
rivers and streams.
Flash Floods
Caused by extremely
intense rainfall, 10 inches
or more an hour, for a
short period of time.
Common in mountainous
areas, where steep slopes
cause water to travel at
high speeds, causing
erosion.
These floods often occur
with little warning.
Is there anything good about a flood?
Floods cause disasters,
but they can also be
beneficial. When a river
overflows, it dumps sand,
silt and debris that is
carried downstream onto
the surrounding land.
After the flood waters
move away, the soil is
more fertile, because of
the organic matter and
minerals that were in the
water.