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THUNDERSTORMS
Convective heavy rain accompanied by lightning and thunder
Ahrens
Thunderstorms
About 1,800 T-storms occur around the world at any instant
Where do they occur the most?
National Lightning Safety Institute
Thunderstorms
Where do they occur the most?
Life cycle of an ordinary thunderstorm cell
Fig. 11.7
THUNDERSTORM
CUMULUS STAGE
• CUMULUS STAGE
• REQUIRES CONTINUOUS SOURCE OF
WARM MOIST AIR
• EACH NEW SURGE OF WARM AIR RISES
HIGHER THAN THE LAST
• STRONG UPDRAFTS
• FALLING PRECIPITATION DRAGS AIR DOWN
- DOWNDRAFT
• ENTRAINMENT
THUNDERSTORM
MATURE STAGE
• SHARP COOL GUSTS AT SURFACE SIGNAL
DOWNDRAFTS
• UPDRAFTS EXIST SIDE BY SIDE WITH
DOWNDRAFTS
• IF CLOUD TOP REACHES TROPOPAUSE
UPDRAFTS SPREAD LATERALLY - ANVIL
SHAPE
• TOP OF ICE LADEN CIRRUS CLOUDS
• GUSTY WINDS, LIGHTNING, HEAVY
PRECIPITATION, HAIL
THUNDERSTORM
DISSIPATING STAGE
• DOWNDRAFT AND ENTRAINMENT
DOMINATE
• NO UPDRAFT
• THUNDERSTORM LOSES ENERGY
SOURCE
Squall line associate with a cold front.
Fig. 11.10a
Schematic of a multicell thunderstorm. Red arrows
represent the warm updraft, blue arrows the cool
downdraft
Fig. 11-10, p. 320
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
UPDRAFTS
CUMULUS STAGE
Dr. M. Pidwirny, Dep. of Geography, Okanagan University College
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
Dr. M. Pidwirny, Dep. of Geography, Okanagan University College
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
NSSL
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
NSSL
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
Thunderstorms
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
DISSIPATING STAGE
DOWNDRAFTS OCCUR
IN THE SAME AREA AS
THE UPDRAFTS
DISSIPATING STAGE (DOWNDRAFTS)
SUPERCELL THUNDERSTORM
• SINGLE CELL THUNDERSTORM THAT
PRODUCES DANGEROUS WEATHER
• REQUIRES A VERY UNSTABLE ATMOSPHERE
AND STRONG VERTICAL WIND SHEAR - BOTH
SPEED AND DIRECTION
• UNDER THE INFLUENCE OF THE STRONG WIND
SHEAR THE ENTIRE THUNDERSTORM ROTATES
• FAVORED REGION IS THE SOUTHERN GREAT
PLAINS IN THE SPRING
TYPE OF THUNDERSTORM
• SINGLE-CELL THUNDERSTORM
• MULTICELL THUNDERSTORM
• MESOSCALE CONVECTIVE C0MPLEX
• SUPERCELL THUNDERSTORM
Fig. 11-33, p. 342
LIGHTNING
• .LARGE ELECTRICAL DISCHARGE THAT RESULTS FROM
RISING AND SINKING MOTIONS IN A THUNDERSTORM
• .SEQUENCE IS AS FOLLOWS;
• .
CHARGE SEPARATION - REALLY DO NOT
UNDERSTAND WHY
• .
GROUND BECOMES POSITIVELY CHARGED
• .
LIGHTNIING FORMATION BEGINS - LEADERS
• .
LIGHTNING FLASH OCCURS
Lightning
formation:
Charge separation.
Fig. 11.28
Fig. 11-37, p. 346
Life cycle and path of a hailstone in a supercell
thunderstorm
Fig. 11-38, p. 346
HAIL
• LARGE CLUMPS OR BALLS OF ICE
• START OF AS A SMALL ICE PARTICLE
• DUE TO UPDRAFT THE ICE PARTICLE DOES NOT
FALL TO GROUND BUT IS RECYCLED INTO THE
FREEZING PORTION OF THE THUNDERSTORM,
• EACH TIME IT IS TAKEN UPWARD IT
ACCUMULATES MORE ICE
• CAN END UP AS LARGE AS A GRAPEFRUIT
Thunderstorms
HAIL
Thunderstorms
HAIL
Thunderstorms
HAIL
Thunderstorms
HAIL
Thunderstorms
1970 Coffeyville KA hailstone
Thunderstorms
HAIL DAMAGE
Thunderstorms
HAIL DAMAGE
Tornados
Distributed by the Disaster Team
Supercourse (www.pitt.edu/~super1)
Author R.T. Schindler
Tornado History
• The “Tri-State Tornado” is
the most violent tornado
on record
• On March 18, 1925, the
tornado formed in Missouri
and traveled 219 miles
across Illinois into Indiana
• The funnel was up to .75
miles across and traveled
as fast as 73 mph.
• It killed approximately 635
people
First Tornado Forecast
On March, 25 1948, Major
Fawbush and Captain Miller
determined that the
conditions of the atmosphere
just west of Tinker AFB, OK
were suitable for tornado
development. The first
tornado forecast ever was
issued. A few hours later, a
tornado arrived causing
significant damage to the
base. However, no deaths
and only a few injuries
occurred because many had
been warned by the tornado
Tornado
A violently rotating column of air
(vortex), hanging from a
cumulonimbus cloud, with
circulation that touches the surface
of the earth
Tornado Formation
Supercell Storm
• Severe weather occurs as strong downbursts…large
hail…occasional flash floods and weak to violent
tornadoes
• Severe event almost always occur near the updraft
interface typically in the rear (southwest) storm flank.
Some of the supercells have the interface on the front of
the southeast flank
• High predictability of occurrence of severe events once a
storm is identified as a supercell
• Extremely dangerous to public
• Extremely dangerous to aviation
The Supercell
Tornado forms here
Tornado Facts
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Tornados can occur almost anywhere in the world
Duration: a few minutes
Diameter (Avg.): 0.4 km
Length of path (Avg.): 6 km
Funnel can travel from 0 mph up to ~70 mph, usually
travels at 30 mph
99% of all tornados in Northern Hemisphere rotate
counterclockwise
Texas is #1 for frequency of tornados per year
Between 1950 and 1995 Texas had 5,722 recorded
tornados
Risk of death in a tornado in Texas: 1 in 1,054,267
Texas cost per person per year for tornados: $3.94
Tornado Myths
• A highway overpass is a safe place to
take shelter under during a tornado
• Opening windows during a tornado will
help balance the pressure between the
inside and outside of the house and may
prevent destruction of the structure
• One should seek shelter in the southwest
corner of a house or basement.
Tornado Oddities
• Tornados are reported to routinely carry
objects many miles and have:
• sucked the frogs out of a pond and dropped
them on a town
• carried a necktie rack with 10 ties attached 40
miles
• carried a flour sack 110 miles from a mill
• Tornados also drive objects into other
objects and have:
• Driven splinters into an iron fire hydrant
• Driven straw and grass into telephone poles
When Tornados Occur
• Anytime of the year- usually
in the spring, summer, and
fall
• Most tornados occur during
late spring in the month of
May
• Between the late afternoon
and early evening is when
most tornados are spawned
• The most dangerous time for
formation during evening
hours
A typical late
afternoon tornado
Songer http://www.pitt.edu/~super1/lecture/lec0761/005.htm
Where Tornados Occur
Tornado Alley covers the Great Plains states
Tornado Wind Speed
In 1971, Dr. Fujita
developed a way of
measuring the winds
of a tornado. He
reasoned that there
was a link between
wind speed and the
damage caused by a
tornado. There are 6
categories of
tornados (F0 – F5)
F0 Category
• (Weak) winds (40-72) mph , little damage
• Damage: tree branches snapped, chimneys
toppled, signs torn down
F3 Category
• (Strong) winds: (158-206) mph, severe damage
• Damage: most trees uprooted, trains
overturned, roofs torn off, walls demolished
F5 Category
• (Violent) winds: (261- 319) mph, incredible damage; rare
Damage: bark peeled off trees, houses lifted off
foundations, vehicles travel greater than 100 m through
the air
Tornado Occurrence by
Category
Tornado Deaths by Category
Tornado Forecasting
Meteorologists who
predict tornado
development analyze the
current atmospheric
conditions such as: air
temp., barometric
pressure, the locations of
fronts, wind velocities,
convection, etc. Probably
the most useful tool a
meteorologist can use to
identify tornados is radar,
specifically Doppler radar
(WSR-88D)
Tornados on Radar
Doppler image of a rain-wrapped tornado
The Life cycle of a Tornado
• The “Life Cycle” of a tornado consists of four
distinct stages.
• These stages were first determined during
the Union City, OK tornado of 1973
• Most tornadic events are difficult to classify
and may not exhibit stages that are obvious
to the observer
• Sometimes events become unclear: one
tornado weakens another appears, or single
event?
• Tornados do not “skip” – gaps in damage
path may indicate a temporary weakening in
intensity
Beginning Stage:
Tornado begins as
a rotating wall cloud
which quickly
evolves into a
funnel
Early Stage:
Tornado funnel develops
(may be transparent) and
extends down from the
cloud to the ground
Mature Stage:
Tornado funnel
reaches maximum
width as well as
maximum intensity
then begins to
shrink
Decay Stage:
tornado may remain
stationary and take on a
ropelike appearance
before dissipating
The Tornado Outbreak of May 3,
1999
• Severe thunderstorms move into Ok,
TX, Ks and spawn estimated 70
tornados, most occurred in Oklahoma
• In Oklahoma 40 people killed, 675
injured
• Damage: $1.2 billion
• Largest tornado outbreak in Oklahoma
history
• 1,780 homes completely destroyed
• 6,550 homes damaged
Satellite image taken May 3, 1999 @ 645 CDT
View from the air of a
tornado path in
Central OK
Tornado near Amber,
OK at 6:30 CDT
Microburst
Microbursts are
downdrafts from
thunderstorms consisting
of a narrow column of
cool air traveling at high
speeds which can cause
damage similar to a
weak tornado over a
small area
Waterspouts
A waterspout is a tornado that forms over a body of
water, or a tornado that moves from land onto water
Storm Chasers
Storm chasers are a group made up of meteorologists
and scientists, as well as amateur observers who
voluntarily put themselves in the path of a severe
thunderstorm in order to hopefully observe a tornado
and obtain photographs and scientific data.
Tornado Indicators
• A greenish colored sky associated with
the thunderstorm (caused possibly by
the scattering of light by particles in the
sky)
• Mammatus clouds
• A sudden drop in barometric pressure
• Large hail of at least .75 in. diameter
• Strong winds > 60 mph
• Frequent and intense lightning
• A rotating wall cloud or a cloud that
appears to hang from the sky
• A loud rumbling noise- seek shelter!
Mammatus clouds
Green sky
Tornado Damage
A 20-ton trailer blown off
U.S. 30; it bounced 5 times
A pick-up truck caught in the
path of a tornado
Tornados mainly cause damage by
picking up something and throwing it
through the air or hurling objects against
something
Early Warning Systems
The National Storm Prediction Center constantly
monitors the weather and radars across the U.S.
They are responsible for issuing tornado watches and
warnings.
• Tornado Watch: a parallelogram is drawn around a
10,000 mi.^2 s area where the atmosphere seems to
possess the conditions necessary for tornado
development (severe thunderstorm)
• Tornado warning: a county has a thunderstorm which
appears to have produced a tornado or someone has
physically spotted a tornado, apparent funnel, or
observed damage from what could be a tornado!
SEEK SHELTER IMMEDIATELY!!