Transcript Weather - Ms. Racette`s Wiki

Weather
Part 6: Storms
What Is a Storm?
• A violent disturbance in the atmosphere
• Marked by sudden changes in air pressure
and high winds
• May cover a large or small area
Rainstorms and Snowstorms
• Happen when two
different fronts
collide
• When a warm front
meets a cold front
nimbostratus clouds
form
• Precipitation falls as
rain if it is warm and
as snow if it is cold
http://www.flickr.com/photos/24841050@N00/2684722
Ice Storm
• When heavy rain
falling over a wide
area freezes on
contact, resulting in a
layer of ice coating
everything
• Can cause great
damage by knocking
down trees and
power lines
Blizzard
• A severe snowstorm
with sustained wind
speeds, or frequent
gusts, greater than
56 km/h (35 mph),
that lasts for 3 or
more hours
• May be accompanied
by severe cold and
large amounts of
drifting snow
'Description:''' Standing tall on North
Dakota snow A March blizzard nearly
buried utility poles. Caption jokingly read
"I believe there is a train under here
somewhere!" *'''Source:'''
http://www.photolib.noaa.gov/historic/n
ws/wea00958.htm *'''Image I
Thunderstorms
• Heavy rainstorms
accompanied by
thunder and lightning
• May also have violent
downdrafts and wind
shear (a great change
in wind speed over a
short distance) that
are hazards for
planes
• Occur when a cold
front moves in and
meets a warm front
causing the
formation of
cumulonimbus
clouds
Thunderstorms
Lightning occurs when
areas of positive and
negative electric
charges build up in the
storm clouds and
discharge suddenly
License: Some rights
reserved by Boby Dimitrov
Thunderstorms
Thunder occurs
because the lightning
superheats the air
causing it to expand
rapidly and create
sound waves.
License: Some rights
reserved by Boby Dimitrov
Thunderstorms
Since light travels
much faster than
sound, there is about a
5 seconds per mile
delay between seeing
the lightning and
hearing the thunder, or
3 s/km.
License: Some rights
reserved by Boby Dimitrov
Thunderstorms
• Lightning striking the
ground is the leading
cause of forest fires
in the western states.
• More people are
killed by lightning
than by any other
type of violent
storm.
License: Some rights
reserved by Boby Dimitrov
Thunderstorm Safety FYI
• Seek shelter before an approaching thunderstorm Lightning can strike as far as 10 miles away from where
it is raining. That’s about the distance you can hear
thunder. If you can hear thunder, you are within striking
distance. Seek shelter immediately! Get inside a home,
large building, or an all-metal (not convertible)
automobile. When thunder roars, go indoors!
• Do not stand underneath a natural lightning rod such
as a tall, isolated tree or a telephone pole.
• Avoid projecting above the surrounding landscape; for
example, do not stand on a hilltop.
• In a forest, seek shelter in a low area under a thick
growth of small trees. In open areas, go to a low place
such as a ravine or valley.
Thunderstorm Safety FYI
• Get away from open water, tractors and other metal farm
equipment, and small metal vehicles such as motorcycles,
bicycles, and golf carts.
• Avoid metal including wire fences, clotheslines, metal pipes
and rails; put down golf clubs.
• Things to avoid while indoors - While inside, stay off land
lines or corded phones, computers and other electrical
equipment that put you in direct contact with electricity. Stay
away from indoor and outdoor pools, bathtubs, showers, and
other plumbing. When inside, wait 30 minutes after the last
sound of thunder and lightning before going out again.
• Safe Shelter from Storms - A house or other substantial
building offers the best protection from lightning. For a
shelter to provide adequate protection from lightning, it must
contain a mechanism for conducting the electrical current
from the point of contact to the ground (ie. wiring, plumbing,
metal gutters and downspouts, etc.).
Thunderstorm Safety FYI
• Unsafe Sheltering - Unless specifically designed to be lightning
safe, small structures do little, if anything to protect people
from lightning. A shelter that does not contain plumbing or
wiring throughout, or some other mechanism for grounding
from the roof to the ground is not safe. Small wooden, vinyl or
metal sheds offer little or no protection from lightning and
should be avoided during thunderstorms.
• Protect Your Pets - Outside dog houses are not lightning-safe.
Dogs that are chained to trees or wire runners can easily fall
victim to lightning strikes. Consider bringing your pets inside
the home or garage during thunderstorms.
• Finally, if you are caught out in a level field or in the open,
away from shelter, and you feel your hair stand on end,
lightning may be about to strike you. Drop to your knees and
bend forward, putting your hands on your knees. Do not lie
flat on the ground.
Sources: http://www.crh.noaa.gov/lmk/?n=weathersafetyrules
http://www.weathersafety.ohio.gov/thunderstormsandlightningsafety.aspx
Cyclones
• Cyclones form around
areas of low pressure
• Contain rising warm air
• Winds spiral around
and into the center in a
counterclockwise
direction in the
Northern Hemisphere,
due to the _________.
• Usually cause rainy,
stormy weather
Original caption from NASA: "A beautifully-formed low-pressure
system swirls off the southwestern coast of Iceland, illustrating
the maxim that "nature abhors a vacuum." The vacuum in this
case would be a region of low atmospheric pressure. In order to
fill this void, air from a nearby high-pressure system moves in, in
this case bringing clouds along for the ride….”
Anticyclones
• High pressure areas
• Winds spiral around
and out from center,
clockwise in the
Northern
Hemisphere
• Weather is usually
clear, dry, and fair.
A Unusual Anticyclone in Southern Australia.
Satellite loop at the time the image above was
taken, showed the Anticyclone was spinning
counterclockwise, as it is in the Southern
Hemisphere.
Hurricanes
• A type of tropical
cyclone
• A tropical cyclone is a
low pressure system
with an organized
circulation that
develops over the
tropical or
subtropical waters.
Tropical Cyclones have
different names
depending on where
they form:
• Hurricanes - Atlantic
and Eastern Pacific
oceans
• Typhoons -Western
Pacific
• Cyclones – Indian
ocean
Hurricanes
• Definition: An intense
• Storm surge: water is
tropical weather system with pushed toward the
a well defined circulation
shore by the force of the
and maximum sustained
storm winds, which can
winds of 74 mph (64 knots)
cause hurricane storm
or higher.
tides with a mean water
level 15 feet or more
• Powered by heat from the
above normal, and then
sea so require ocean
wind driven waves are
temperatures of at least
superimposed on the
80ºF or 27ºC to form
storm tide.
• Eye: center of the hurricane
• Coastal damage can be
where winds are calm
particularly severe due
• Hurricane damage is caused
to storm surge
by high winds and large
amounts of rain.
Hurricane Categories
• Saffir/Simpson
Hurricane Scale
• 5 categories based
primarily on wind
speeds
• Scale includes
estimates for
associated storm
surge and barometric
pressure for each
level
Categories (wind speeds):
• 1 – Minimal (74-95 mph)
• 2 – Moderate (96-110
mph)
• 3 – Extensive (111-120
mph)
• 4 – Extreme (130 – 156
mph)
• 5 – Catastrophic (157
mph or higher)
See animation at http://www.nhc.noaa.gov/aboutsshws.php
Hurricanes
• Read about how hurricanes are named at
http://www.nhc.noaa.gov/aboutnames.shtml
• Hurricane Hunters video:
http://oceantoday.noaa.gov/hurricanehunters/
• The 2012 Atlantic Hurricane Season in 4.5 Minutes
• Formation of a Hurricane
• Hurricanes are the most powerful storms on Earth in terms of
total energy involved.
Tornadoes
• A narrow, violently
rotating column of air
that extends from the
base of a thunderstorm
to the ground.
• Becomes visible when it
forms a condensation
funnel made up of
water droplets, dust and
debris.
• Most violent of all
atmospheric storms.
Tornadoes
• The strength of a
tornado is accessed
after the fact by the
amount of damage it
caused.
• Enhanced F-scale
rates tornadoes as F0
to F5
• Wind speed can only be
directly measured for
the weakest of
tornadoes.
• The highest speed ever
remotely measured was
302 mph, the highest
wind speed ever
detected near the
Earth’s surface.
Tornado Alley
• “Tornado Alley is a
nickname in the popular
media for a broad swath
of relatively high tornado
occurrence in the central
U. S.
• Violent or killer tornadoes
do happen outside this
Tornado Alley every year.
• Tornadoes can occur
almost anywhere in the
U. S., including west of
the Rockies and east of
the Appalachians.”
Source: http://www.spc.noaa.gov/faq/tornado/
Tornadoes
• Read Tornado Facts
at
http://www.scienceki
ds.co.nz/sciencefacts
/weather/tornado.ht
ml
• Video:http://www.yo
utube.com/watch?fe
ature=player_embed
ded&v=43VoMesUd2
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