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Home , Funnel cloud, Tornado climatology, Wall cloud

Chapter 11 – Lightning, Thunder and Tornadoes

Understanding Weather and Climate Aguado and Burt

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Bolt From the Blue

Photo Courtesy of John Schroeder ATMO 1300

1 Lightning

• Lightning occurs when a voltage gradient in the (s)/ground overcomes the electrical resistance of the air.

•Types: – Cloud to cloud (CC) – Cloud to ground (CG)

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Charge Separation

• Positive charges accumulate in the upper portions and negative charges in the lower portions of the cloud. – Exact cause unknown! – Lightning only occurs in that extend above the freezing level.

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2 Lightning Facts

• Electrical current – 20,000 A • Temperature – 54,000°F • Total Power Transfer – 100-watt light bulb for a minute

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Cloud to Ground Lightning

• Stepper Leader – invisible downward leader • Spark from the Ground – completing pathway for flow of electrons • Return Stroke – brightly illuminated, transfer positive charge from surface to cloud base • Dart Leader – repetitive process to remove remaining negative charge at cloud base

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3 Thunder

• Thunder is caused as air explosively expands in response to the extreme heat of lightning. • The speed of sound is slower than the speed of light, thus there is often a lag between the lightning and the resultant thunder.

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Air Mass

•Life Cycle – Cumulus Stage – Mature Stage – Dissipative Stage

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4 Severe Thunderstorms

• speeds in excess of 58 mph • larger than 0.75 inches • or

•Types: – Mesoscale Convective Systems (MCS) • Lines, Mesoscale Convective Complexes (MCC) – Thunderstorms

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Severe Thunderstorms

• Severe thunderstorms require: – – High water vapor content in the lower – A trigger mechanism – Potential instability

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5 Potential Instability

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Mesoscale Convective Complexes

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6 Squall Lines on Radar

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Squall Lines

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7 Bowing

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Supercell

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8 Formation

• Dependent on vertical wind shear • Updrafts tilt horizontal tubes vertically • Stretching of the vortex tube provides a narrowing column of rotating air • Can lead to wall clouds, funnel clouds and tornadoes

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Mesocyclone Formation

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9 Supercell Thunderstorm

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Supercell Thunderstorm

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10 Doppler Radar Detection of Supercell Thunderstorms

ATMO 1300 http://www.usatoday.com/weather/tg/wsupercl/wsuprcl1.htm

Mesocyclone Detection

Air Motion Towards the Observer Air Motion Away From the Observer

Incoming = Green Colors Outgoing = Red Colors

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11 ATMO 1300

Supercell Structure

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12 Upper Level Flow

Anvil Back Sheared Anvil

Updraft

Photo Courtesy of Jeremy Massey, Ralls/Crosbyton May 27, 2002ATMO 1300

Updraft

Forward Flank Free Downdraft Updraft Base

Wall Cloud ATMO 1300

13 Forward Flank Downdraft Updraft

Wall Cloud

John Schroeder, Muleshue, June 3, 2003 ATMO 1300

Rear Flank Downdraft

Forward Flank Downdraft Updraft

Wall Cloud

ATMO 1300 John Schroeder, Near Dalhart Texas, May 15, 2003

14 Thunderstorm Climatology

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15 Detailed Reflectivity Data

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Detailed Reflectivity Data

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16 ATMO 1300 John Schroeder, Near Dalhart Texas, May 15, 2003

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17 Tornado Climatology

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Tornado Climatology

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18 Tornado Climatology

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Tornado Climatology

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19 Tornado Climatology

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Tornado and Supercell Thunderstorm

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20 Tornado and Supercell Thunderstorm

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Tornado Damage

• Buildings do not explode • and windborne debris are primary causes for property damage and loss of life. – Do not open your window

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21 Tornado Damage

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Watches and Warnings

• Watch – the atmosphere is conducive to producing and/or tornadoes – Issued by Prediction Center (SPC) • Warning – Doppler radar or a storm spotter has indicated that severe weather and/or a tornado is occurring or probable – Issued by local (NWS) office.

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