Transcript 3.2 Notes: Low-pressure systems can become storms

Severe Weather
Thunderstorms
• Small intense systems that can produce
strong winds, rain, lightning and thunder.
• Need 2 conditions
– Air near surface needs to be warm and
moist
– The atmosphere must be unstable
Becoming unstable…
• The surrounding air is colder than the
rising air mass
– This makes that rising air CONTINUE rising
• The thunderstorm occurs when the air is
rising rapidly
– Forms cumulonimbus cloud
Lightning!
• Electrical charges build up near the tops and bottoms
of clouds heading from positive to negative to positive
(opposites attract)
• Flash of light occurs when a charge sparks
• The flash heats the air to about the temperature of
the surface of the sun
• ENERGY IS RELEASED
Effects
• Thunderstorms can have positive or negative
effects
• Positive – rain can provide water for crops and
restore lakes and streams
• Negative
– Flash floods
– Winds
– Hail
– Lightning
Funnel Cloud v. Tornado
• Wind traveling in 2 different directions causes
it to start spinning
• The updrafts of air push the spinning column
down, sometimes to the ground
• It is called a tornado once it hits the ground
Funnel cloud
Tornado
Tornadoes
• Cumulonimbus clouds can sometimes
form tornadoes
• Only 1 percent of thunderstorms form
tornadoes
Formation
• About 75 percent of tornadoes happen in the
United States.
– Warm humid air comes up from the Gulf of
Mexico and meets cold dry air from
Canada in the plains.
Effects
• Winds usually average around 95mph
• Most are small and last only a few minutes
• Larger ones are less common (20%) are strong
enough to knock over trees, lift cars or take roofs
off houses.
• Very few (1%) are violent enough to lift or
completely demolish sturdy buildings and can last
more than two hours
Path
• A tornado moves along with its
thunderstorm, it travels fast and weaves
a path that is impossible to predict
• Tornado watch
• When the weather conditions might
produce tornadoes.
• Tornado warning
• When a tornado has
been detected
Hurricanes
• Most powerful storms on Earth
• Different names
– Typhoons – Pacific Ocean
– Cyclones – Indian Ocean
• Form over warm tropical oceans
– 5o – 20o North and South
• Vary in size
– 160 km to 1,500 km in diameter
• Can travel thousands of miles
Formation of Hurricanes
• Hurricane Season – August to October
• Begins as a group of thunderstorms
• Energy
– Comes from condensed water vapor
– Energy moves from ocean water into the air
• Strong Winds Develop
– Coriolis effect bends the wind
• Fuel
– Direct contact with warm ocean water
• Hurricanes will continue to grow until they
lose their source of warm, moist air
Hurricane Features
Effects of Hurricanes
• Wind Speed
– 120 km/h to 300 km/h
• Can cause damage in a variety of ways
• Lift Cars
• Produce tornadoes
• Uproot Trees
• Tear roofs off buildings
• Heavy rains cause rivers to overflow
• When a hurricane moves into a coastal area it causes a
storm surge
– Storm surges can rise sea level and have large waves (1m to 8m)
• National Hurricane Center tries to warn people in time.
Winter Storms
• Formed when two air masses collide.
• A continental polar air mass forming over snow is
especially cold, dry, and dense.
– It forces moist air to rise very quickly.
Blizzards
• A storm with falling or blowing snow, winds
at least 35 mph, reduced visibility and intense
cold.
• Occur in many parts of the Northern and
Central United States.
Formation of a Blizzard
1. When warm air collides with cold
air and is forced to rise above the
colder air, the warm air brings
moisture.
2. This moisture is formed normally
by the wet air moving from the
South or by blowing across large
bodies of water.
3. A lift is created to raise moist air
to form clouds and create ice and
snow.
Duration of a Blizzard
• For a storm to be considered a blizzard it
has to last at least 3 hours.
• Some blizzards can last for a few hours or
even days!
Dangers of Blizzards
• Whiteout conditions make it hard to see when
traveling.
• Strong winds and cold temperatures can create
dangerous wind chill temperatures.
• Roads can be slippery to drive on.
• Power outages can occur due to strong winds and
heavy snow.
• Pipes can freeze and fuel
sources can be cut off.
Dust Storm
• Strong, violent winds that carry fine
particles like silt, clay, sand and dust-filled
air over an extensive area.
Formation of a Dust Storm
• Any area with a lot of dust and sand particles
– Need dry air – No precipitation or water vapor in the air
– Lots of wind
• Huge
– Can spread over hundreds of miles
• Powerful
– Wind speeds of at least 25 miles per hour (40 km)
Dangers of a Dust Storm
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Arrive without warning
Create large wall of dust and debris.
Last only a few minutes
Leave debris behind
Hard to see during storm
Breathing is impacted.
Takes fertile top soil away and
reduces future crops.
• Current crops are covered with dust.