Public Information Statement
Issued by NWS Shreveport, LA

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NOUS44 KSHV 241054
PNSSHV
ARZ050-051-059>061-070>073-LAZ001>006-010>014-017>022-OKZ077-
TXZ096-097-108>112-124>126-136>138-149>153-165>167-250300-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE SHREVEPORT LA
554 AM CDT TUE JUN 24 2014

...PUBLIC INFORMATION STATEMENT...

...UNDERSTANDING THE SCIENCE OF THUNDERSTORMS AND LIGHTNING...

BY DEFINITION...ALL THUNDERSTORMS CONTAIN LIGHTNING. LIGHTNING IS
A GIANT SPARK OF ELECTRICITY THAT OCCURS WITHIN THE ATMOSPHERE OR
BETWEEN THE ATMOSPHERE AND THE GROUND.  AS LIGHTNING PASSES THROUGH
THE AIR...IT HEATS THE AIR RAPIDLY TO A TEMPERATURE OF ABOUT 50000
DEGREES FAHRENHEIT...CONSIDERABLY HOTTER THAN THE SURFACE OF THE
SUN. DURING A LIGHTNING DISCHARGE...THE SUDDEN HEATING OF THE AIR
CAUSES IT TO EXPAND RAPIDLY.   AFTER THE DISCHARGE...THE AIR
CONTRACTS QUICKLY AS IT COOLS BACK TO A NORMAL TEMPERATURE.  THIS
RAPID EXPANSION AND CONTRACTION OF THE AIR CAUSES A SHOCK WAVE THAT
WE HEAR AS THUNDER...THIS SHOCK WAVE CAN DAMAGE WALLS AND BREAK
GLASS.

LIGHTNING CAN OCCUR COMPLETELY WITHIN THE THUNDERSTORM CLOUD OR
BETWEEN THE CLOUD AND THE GROUND. IN CLOUD LIGHTNING GENERALLY
OCCURS BETWEEN POSITIVE CHARGES NEAR THE TOP OF THE CLOUD AND
NEGATIVE CHARGES NEAR THE BOTTOM OF THE CLOUD. CLOUD TO GROUND
LIGHTNING OCCURS BETWEEN THE CLOUD AND THE GROUND AND IS...OF
COURSE...THE MOST DANGEROUS.  LIGHTNING CAN ALSO OCCUR BETWEEN
CLOUDS.

CLOUD TO GROUND LIGHTNING CAN BE CATEGORIZED INTO TWO DIFFERENT
TYPES...THE NEGATIVE FLASH AND THE POSITIVE FLASH.  THE NEGATIVE
FLASH USUALLY OCCURS BETWEEN THE NEGATIVE CHARGES IN THE LOWER PART
OF THE STORM AND THE POSITIVE CHARGES ON THE GROUND UNDER AND NEAR
THE CLOUD BASE.  POSITIVE FLASHES USUALLY OCCUR BETWEEN THE
POSITIVELY CHARGED UPPER LEVELS OF THE STORM AND THE NEGATIVELY
CHARGED AREA SURROUNDING THE STORM.

LIGHTNING IS FASCINATING TO WATCH BUT ALSO EXTREMELY DANGEROUS.
UNDERSTANDING THE DANGERS OF LIGHTNING AND HOW IT FORMS IS VERY
IMPORTANT SO THAT YOU CAN GET TO A SAFE PLACE WHEN THUNDERSTORMS
THREATEN.

JUST REMEMBER...WHEN THUNDER ROARS...GO INDOORS.

$$

11/20





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