Download Weather 2

II. Severe Weather
A. Thunderstorms
1. Form at a cold front- warm air is pushed
upwards by cold, dense air.
2. Warm, moist air rises higher in the
atmosphere and condenses into clouds
3. Cumulonimbus clouds form; rain droplets
get carried up and down through the
cloud by winds, and fall as heavy rain.
4. Thunderstorms may bring heavy rains,
hail, sometimes snow, and thunder
and lightning! They don’t usually last
for very long. (half an hour)
5. Lightning- when different parts of a
cloud build up opposite charges,
electricity flows between them. This is
lightning!
a) when a charge builds up in a
cloud, it may discharge to the
ground
http://www.ultraslo.com/page/368032211
6. Thunder- occurs when lightning heats
the air (over 30,000 degrees F).
a)air expands quickly, then it cools
very quickly and contracts
b) Rapid movement of molecules
forms sound waves
B. Tornadoes
1. When a severe thunderstorm
occurs (winds over 89 km/h),
a tornado may result
2. A tornado is a violently
rotating column or air that
contacts the ground
3. Can rip apart buildings,
uproot trees, lift up cars, and
cause major damage and harm.
4. Tornadoes are measured on the Fujita
Scale. It ranks tornadoes by how much
damage they cause.
C. Hurricanes
1. A large, swirling lowpressure system that forms
over a warm ocean
2. Also called typhoons or
cyclones, they must have
winds of 119 km/h to be a
hurricane.
3. Hurricanes start as low-pressure storms,
then gain power from the moisture
and warmth of ocean water
4. They travel west towards North
America, gaining power as they come
5. When they hit land, they lose the
warm moisture from the ocean, and
begin to die out.
6. High winds and flooding can cause
lots of damage.
7. High winds hitting the water cause the
ocean to bulge upwards (storm surge)
Q: Since hurricanes need warm water to
grow stronger, during which seasons
would you likely see hurricanes?
A: Summer and Autumn (Fall)
8. Saffir-Simpson Scale- classifies
hurricanes based on their wind speed
and storm surges.
a) tries to predict possible damages
Identify some patterns you can
see in this data table.
D. Blizzards
1. Blizzards have a few criteria:
a) low-temperature
b) high winds (more than
56 km/h or 35 miles per
hour)
c) visibility less than 400 m
d) falling or blowing snow
e) Lasts for 3 or more hours
E. Floods
1. When water covers the
ground due to heavy rain,
an overflowing lake, or an
overflowing river
2. Sometimes the ground
can’t soak up water fast
enough
3. If the ground isn’t permeable,
water can’t soak in, making floods
4. Concrete, blacktop, and other
manmade surfaces don’t let
water sink into the ground.
http://www.uky.edu/AS/Geology
/howell/goodies/elearning/mod
ule12swf.swf
F. Severe Weather Safety
1. Watch- conditions are
favorable for severe weather
(tornadoes, thunderstorms,
floods, blizzards, hurricanes).
Stay tuned for more info.
2. Warning- a severe weather
condition already exists. Take
immediate action!
During a tornado or
thunderstorm warning:
Take shelter in the basement, or
middle of the building away
from windows.
Hurricane or flood Warning:
Be prepared to leave, move
inland to higher ground
For a Blizzard warning, STAY
INDOORS! Being outside too long
can give you frostbite, and you
can get lost in the blinding snow!