Public Information Statement
Issued by NWS Riverton, WY

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NOUS45 KRIW 241350
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WYZ001>020-022>030-251200-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE RIVERTON WY
750 AM MDT TUE JUN 24 2014

...HOW DOES LIGHTNING FORM?...

LIGHTNING SAFETY AWARENESS WEEK CONTINUES TODAY. DID YOU KNOW THAT AT
ANY GIVEN MOMENT THERE ARE AROUND 1800 THUNDERSTORMS IN PROGRESS
SOMEWHERE ON THE EARTH?

THUNDERSTORMS FORM IN THE ATMOSPHERE WHEN THERE IS MOISTURE...
INSTABILITY...AND A TRIGGER SUCH AS A COLD FRONT TO CAUSE THE AIR
TO RISE.  CONTINUED RISING MOTIONS WITHIN THE STORM MAY BUILD THE
CLOUD TO A HEIGHT OF 35,000 TO 60,000 FEET (6 TO 10 MILES).
TEMPERATURES HIGH IN THE ATMOSPHERE ARE VERY COLD...AND ICE FORMS
IN THE HIGHER PARTS OF THE CLOUD.  THE FORMATION OF ICE IN A CLOUD
IS A VERY IMPORTANT ELEMENT IN THE DEVELOPMENT OF LIGHTNING.  WITHIN
A STORM THERE ARE COLLISIONS BETWEEN ICE PARTICLES...WHICH CAUSE A
SEPARATION OF ELECTRICAL CHARGES.  POSITIVELY CHARGED ICE CRYSTALS
RISE TO THE TOP OF THE THUNDERSTORM...AND NEGATIVELY CHARGED ICE
PARTICLES DROP TO THE LOWER PART OF THE STORM.

A MOVING THUNDERSTORM GATHERS POSITIVELY CHARGED PARTICLES ALONG THE
GROUND.  AS THE DIFFERENCES IN CHARGES CONTINUE TO INCREASE BETWEEN
THE CLOUD AND THE GROUND...POSITIVELY CHARGED PARTICLES RISE UP
TALLER OBJECTS SUCH AS TREES...HOUSES...AND TELEPHONE POLLS.  THE
NEGATIVELY CHARGED AREA IN THE STORM WILL SEND OUT A CHARGE TOWARD
THE GROUND CALLED A STEPPED LEADER.  IT IS INVISIBLE TO THE HUMAN
EYE...AND MOVES IN STEPS IN LESS THAN A SECOND TOWARD THE GROUND.
WHEN IT GETS CLOSE TO THE GROUND...IT IS ATTRACTED BY POSITIVELY
CHARGED OBJECTS...AND A CHANNEL DEVELOPS.  YOU SEE THE ELECTRICAL
TRANSFER IN THIS CHANNEL AS LIGHTNING.

THE LIGHTNING CHANNEL HEATS RAPIDLY TO NEARLY 50,000 DEGREES
FAHRENHEIT.  THE RAPID EXPANSION OF HEATED AIR CAUSES THUNDER.
SINCE LIGHT TRAVELS FASTER THAN SOUND IN THE ATMOSPHERE...THE SOUND
WILL BE HEARD AFTER THE FLASH OF LIGHTNING.  IF YOU ARE EVER IN A
STORM WHEN YOU SEE THE LIGHTNING AND HEAR THE THUNDER AT THE SAME
TIME...THAT LIGHTNING IS IN YOUR NEIGHBORHOOD!

SOME LIGHTNING ORIGINATES IN THE CIRRUS ANVIL AT THE TOP OF THE
THUNDERSTORM.  THIS AREA CARRIES A LARGE POSITIVE CHARGE...AND
LIGHTNING FROM THIS AREA IS CALLED POSITIVE LIGHTNING.  THIS TYPE IS
PARTICULARLY DANGEROUS BECAUSE IT FREQUENTLY STRIKES AWAY FROM THE
MAIN THUNDERSTORM.  IT CAN STRIKE AS FAR AS 10 MILES FROM THE
STORM...IN AREAS THAT MOST PEOPLE DO NOT CONSIDER TO BE A LIGHTNING
RISK AREA.

FOR YOUR LOCAL FORECAST OR MORE INFORMATION ON LIGHTNING AWARENESS...
GO TO THE NWS RIVERTON HOMEPAGE AT:

WEATHER.GOV/RIVERTON

$$



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