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!!