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Storms
Storms
 Storms vary immensely depending on whether
they’re:
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warm or cold,
coming off the ocean or off a continent,
occurring in summer or winter, and many other factors.
 The effects of storms also vary depending on
 whether they strike a populated area or a natural landscape.
How do Thunderstorms Form?
 Thunderstorms form when ground temperatures are
high

ordinarily in the late afternoon or early evening in spring and
summer.
(a) As temperatures increase,
warm moist air rises.
 Cumulus and then
cumulonimbus clouds form.
(b) Winds at the top of the stratosphere
blow the cloud top sideways to make the
anvil shape that characterizes a cloud as
a thunderhead.
Convection in the Clouds
 Water vapor condenses, releasing latent
heat inside the cloud. This makes the air
inside the cloud warmer than the air
outside the cloud.
 Water droplets rise through the cloud in
updrafts, cool, collect, then fall to create a
downdraft.
 Downdrafts cool the air at the base of the
cloud, so the air is no longer warm enough
to rise.
 As a result, convection shuts down.
 Without convection, water vapor does
not condense, no latent heat is released,
and the thunderhead runs out of energy.
Thunder and Lightning
 Lightning
 Forms when energy collects in
cumulonimbus clouds then is released
as electricity.
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http://video.nationalgeographic.com/video/enviro
nment/environment-natural-disasters/landslidesand-more/lightning/
 Thunder
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Forms when lightning heats the air so
that it expands explosively.
Sound travels slower than light, so we
hear thunder after we see lightning.
Tornadoes
 are violently rotating columns of air that descend
from a thunderstorm to the ground.
 form at the front of severe thunderstorms
 The average wind speed is about 110 mph
 Travels over the ground at about 28 mph
 Goes about 16 miles before losing energy and
disappearing
 Most injuries and deaths from tornadoes are caused
by flying debris.
Predicting Tornadoes
 Meteorologists can only predict tornado danger over a very wide region.
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No one can tell exactly where and when a tornado will touch down.
The exact path is unknown because tornado movement is not very
predictable.
Watch vs. Warning
 Tornado Watch- conditions are favorable for
severe thunderstorms to form; may be capable of
producing a tornado
 Tornado Warning- issued once a tornado is
sighted on radar, its path is predicted and a warning
is issued to people in that area.
3D radar of the Moore,
Okla., tornado from May
2013
Measuring Tornado Intensity
 The intensity of tornadoes is measured on the Fujita Scale
which assigns a value based on wind speed and damage.
Cyclones
 Cyclone:
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winds rotate
counterclockwise in the
Northern Hemisphere
around a center of low
pressure
The swirling air rises and
cools, creating clouds and
precipitation.
 Anticyclone:
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winds rotate clockwise in
the Northern Hemisphere
around a center of high
pressure
Air sinks to the ground.
High pressure centers
generally have fair
weather.
Two Types of Cyclones
 Mid-latitude cyclones: are the main cause of
winter storms in the middle latitudes.
 The air twists, rotating counterclockwise in the
Northern Hemisphere and clockwise in the Southern
Hemisphere.
Northern Hemisphere
Southern Hemisphere
Mid-latitude Cyclones
 Especially fierce in the mid-Atlantic and New
England states where they are called nor’easters,
because they come from the northeast.
Two Types of Cyclones
 Tropical cyclones: also known as
 hurricanes in the North Atlantic and eastern Pacific oceans
 typhoons in the western Pacific Ocean
 tropical cyclones in the Indian Ocean
 willi-willi's in the waters near Australia
 Tropical cyclones can be large and damaging
Formation
 Like giant engines that
use warm, moist air as
fuel.
 That is why they form
only over warm ocean
waters near the equator.
 The warm, moist air over
the ocean rises upward
from near the surface.
 Air from surrounding areas with higher air pressure pushes
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in to the low pressure area.
Then that "new" air becomes warm and moist and rises,
too.
As the warm air continues to rise, the surrounding air
swirls in to take its place.
As the warmed, moist air rises and cools off, the water in
the air forms clouds.
The whole system of clouds and wind spins and grows, fed
by the ocean's heat and water evaporating from the surface.
 As the storm system rotates faster and faster, an eye
forms in the center.
 It is very calm and clear in the eye, with very low air
pressure.
 Higher pressure air from above flows down into the
eye.
Saffir - Simpson Hurricane Scale
Category
Mph
Estimated Damage
1 (weak)
74-95
Above normal; no real damage to structures
2 (moderate)
96-110
Some roofing, door, and window damage,
considerable damage to vegetation, mobile
homes, and piers
3 (strong)
111-130
Some buildings damaged; mobile homes
destroyed
131-156
Complete roof failure on small residences;
major erosion of beach areas; major damage to
lower floors of structures near shore
>156
Complete roof failure on many residences and
industrial buildings; some complete building
failures
4 (very strong)
5 (devastating)
•
NASA IN
KATRINA'S
WAKE
 Damage can occur
through:
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Strong winds
Storm surge
Flooding
Tornadoes
Rip tides
 Even when the hurricane
Flooding in New Orleans after
Hurricane Katrina caused the
levees to break and water to pour
through the city.
has yet to make landfall,
its effects can be
dangerous.
https://www.youtube.com/watch?v=
ta7mwA4ZwHs
Blizzards
 Specific conditions for this classification:
 Temperatures below –7°C (20°F); –12°C (10°F) for a
severe blizzard.
 Winds greater than 35 mph; 45 mph for a severe
blizzard.
 Snow so heavy that
visibility is 1/4 mile or
less for at least three hours;
near zero visibility for a
severe blizzard.
 Lake-effect snow forms as the frigid air travels across
one of the Great Lakes, it warms and absorbs moisture.
 When the air mass reaches the leeward side of the lake, it is
very unstable and it drops tremendous amounts of snow.
Lake-effect snow falls on the snowiest,
metropolitan areas in the United States:
Buffalo and Rochester, New York
Michigan
Heat Wave
 is a long period of hot weather, at least 86°F (30°C)
for at least three days in cooler locations, but much
more in hotter locations.
 Can form when a high pressure zone keeps the jet
stream further north than normal.
Drought
 a prolonged period of abnormally low rainfall; a shortage
of water resulting from this.
 During times of Drought:
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vegetation is visibly dry
stream flows decline
water levels in lakes and reservoirs fall
the depth to water in wells increases
 Long Term Impacts:
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groundwater level declines
land subsidence
seawater intrusion
damage to ecosystems