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THUNDERSTORMS
Convective heavy rain accompanied by lightning and thunder
Ahrens
ThunderstormsAbout 1,800 T-storms occur around the world at any instant
Where do they occur the most?
National Lightning Safety Institute
ThunderstormsWhere do they occur the most?
Fig. 11.7
Life cycle of an ordinary thunderstorm cell
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
Fig. 11.10a
Squall line associate with a cold front.
Fig. 11-10, p. 320
Schematic of a multicell thunderstorm. Red arrows represent the warm updraft, blue arrows the
cool downdraft
Thunderstorms
CUMULUS STAGEDr. M. Pidwirny, Dep. of Geography, Okanagan University College
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
UPDRAFTS
Thunderstorms
MATURE STAGEDr. M. Pidwirny, Dep. of Geography, Okanagan University College
ORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
ThunderstormsORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGENSSL
ThunderstormsORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGENSSL
ThunderstormsORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
ThunderstormsORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
MATURE STAGE
ThunderstormsORDINARY, AIR MASS, SINGLE CELL* THUNDERSTORMS
DISSIPATING STAGE
DOWNDRAFTS OCCURIN 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
Fig. 11.28
Lightning formation: Charge separation.
Fig. 11-37, p. 346
Fig. 11-38, p. 346
Life cycle and path of a hailstone in a supercell
thunderstorm
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
ThunderstormsHAIL
ThunderstormsHAIL
ThunderstormsHAIL
Thunderstorms1970 Coffeyville KA hailstone
ThunderstormsHAIL DAMAGE
ThunderstormsHAIL DAMAGE
Tornados
Author R.T. SchindlerDistributed by the Disaster TeamSupercourse (www.pitt.edu/~super1)
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 forecast.
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• 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
Tornados mainly cause damage by picking up something and throwing it through the air or hurling objects against something
A 20-ton trailer blown off U.S. 30; it bounced 5 times
A pick-up truck caught in the path of a tornado
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!!