Skip Navigation Linksweather.gov   
NOAA logo - Click to go to the NOAA homepage National Weather Service Forecast Office   NWS logo - Click to go to the NWS homepage
NWS Newport/Morehead City, NC
 

Local forecast by
"City, St" or zip code
  
National Lighting Safety Awareness Week
June 21-27, 2009


Lightning kills or injures hundreds each year. There have been 9 deaths in just the first half of June alone! Explore the wealth of resources on the NWS lightning safety website.

Monday    Tuesday    Wednesday    Thursday    Friday   


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

THE NATIONAL WEATHER SERVICE HAS DECLARED THE WEEK OF JUNE 21ST
THROUGH JUNE 27TH, LIGHTNING SAFETY AWARENESS WEEK. THIS IS THE
SECOND IN A SERIES OF FIVE PUBLIC INFORMATION STATEMENTS TO BE
ISSUED BY THE NATIONAL WEATHER SERVICE OFFICE IN NEWPORT/MOREHEAD
CITY, NORTH CAROLINA CONTAINING INFORMATION ON LIGHTNING AND
LIGHTNING SAFETY.

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 50,000
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.

ALL THUNDERSTORMS GO THROUGH VARIOUS STAGES OF GROWTH, DEVELOPMENT,
ELECTRIFICATION, AND DISSIPATION. THE PROCESS OF THUNDERSTORM
DEVELOPMENT OFTEN BEGINS EARLY IN THE DAY WHEN THE SUN HEATS THE AIR
NEAR THE GROUND AND POCKETS OF WARMER AIR START TO RISE IN THE
ATMOSPHERE. WHEN THESE POCKETS REACH A CERTAIN LEVEL IN THE
ATMOSPHERE, CUMULUS CLOUDS START TO FORM. CONTINUED HEATING CAN
CAUSE THESE CLOUDS TO GROW VERTICALLY UPWARD INTO THE ATMOSPHERE.
THESE TOWERING CUMULUS CLOUDS MAY BE ONE OF THE FIRST INDICATIONS OF
A DEVELOPING THUNDERSTORM. THE FINAL STAGE OF DEVELOPMENT OCCURS AS
THE TOP OF THE CLOUD BECOMES ANVIL SHAPED.

AS THE CLOUD GROWS, PRECIPITATION FORMS WITHIN THE CLOUD WITH MOSTLY
ICE CRYSTALS IN THE UPPER LEVELS OF THE CLOUD, A MIXTURE OF ICE
CRYSTALS AND HAIL IN THE MIDDLE LEVELS, AND A MIXTURE OF RAIN AND
MELTING HAIL IN THE LOWER LEVELS. DUE TO AIR MOVEMENTS AND
COLLISIONS BETWEEN THE PRECIPITATION PARTICLES NEAR THE MIDDLE OF
THE CLOUD, THE VARIOUS PRECIPITATION PARTICLES BECOME CHARGED. THE
LIGHTER ICE CRYSTALS GATHER A POSITIVE CHARGE AND ARE CARRIED UPWARD
INTO THE UPPER PART OF THE STORM BY THE UPDRAFT. THE HEAVIER HAIL
GATHERS A NEGATIVE CHARGE AND FALLS TOWARD THE LOWER PART OF THE
STORM. THE END RESULT IS THAT THE TOP OF THE STORM BECOMES
POSITIVELY CHARGED AND THE LOWER PART BECOMES NEGATIVELY CHARGED.

NORMALLY, THE EARTH'S SURFACE HAS A SLIGHT NEGATIVE CHARGE. HOWEVER,
AS THE NEGATIVE CHARGES BUILD UP IN THE LOWER PART OF THE STORM, THE
GROUND BENEATH THE BASE OF THE CLOUD AND IN THE AREA IMMEDIATELY
SURROUNDING THE CLOUD BECOMES POSITIVELY CHARGED. AS THE CLOUD
MOVES, THESE INDUCED POSITIVE CHARGES ON THE GROUND FOLLOW THE CLOUD
LIKE A SHADOW. FARTHER AWAY FROM THE CLOUD BASE, BUT UNDER THE
POSITIVELY CHARGED ANVIL, THE NEGATIVE CHARGE MAY BE FURTHER INDUCED.

IN THE INITIAL STAGES OF DEVELOPMENT, AIR ACTS AS AN INSULATOR
BETWEEN THE POSITIVE AND NEGATIVE CHARGES. HOWEVER, WHEN THE
ELECTRICAL POTENTIAL BETWEEN THE POSITIVE AND NEGATIVE CHARGES
BECOMES TOO GREAT, THERE IS A DISCHARGE OF ELECTRICITY THAT WE KNOW
AS LIGHTNING.

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.

IN THE NEGATIVE CLOUD TO GROUND FLASH, AN ALMOST INVISIBLE,
NEGATIVELY CHARGED CHANNEL OF AIR FORMS NEAR THE CLOUD BASE AND
SURGES DOWNWARD TOWARD THE GROUND. AS THIS STEP LEADER APPROACHES
THE GROUND, STREAMERS OF POSITIVE CHARGE SHOOT UPWARD FROM TREES,
BUILDINGS, AND OTHER OBJECTS ON THE GROUND. WHEN THESE STREAMERS
MEET THE STEP LEADER, THE CONNECTION IS COMPLETE, AND A SURGE OF
ELECTRICAL CURRENT MOVES FROM THE GROUND TO THE CLOUD CAUSING THE
VISIBLE RETURN STROKE THAT WE CALL LIGHTNING. THE ENTIRE PROCESS
TAKES ONLY A MATTER OF A SECONDS.

THE PROCESS FOR A POSITIVE FLASH IS SIMILAR EXCEPT THAT A POSITIVE
CHANNEL USUALLY ORIGINATES IN THE ANVIL OF THE STORM AND SURGES
DOWNWARD. IN THIS CASE, STREAMERS OF NEGATIVE CHARGE SHOOT UP TO
MEET POSITIVELY CHARGED CHANNEL AS IT APPROACHES THE GROUND. WHEN A
CONNECTION IS MADE, A POSITIVE FLASH OF LIGHTNING OCCURS.

WHILE BOTH NEGATIVE AND POSITIVE FLASHES OF LIGHTNING CAN BE DEADLY,
THE POSITIVE FLASHES GENERALLY ARE MORE DESTRUCTIVE AND ARE MORE APT
TO CATCH PEOPLE BY SURPRISE. BECAUSE THE DISTANCE BETWEEN THE GROUND
AND ANVIL IS MUCH GREATER THAN THE DISTANCE BETWEEN THE GROUND AND
THE CLOUD BASE, A MUCH LARGER ELECTRIC POTENTIAL IS NEEDED TO
INITIATE A POSITIVE FLASH OF LIGHTNING. FOR THE SAME REASON,
POSITIVE FLASHES ARE INFREQUENT AND WIDELY SCATTERED AROUND THE
STORM, BUT GENERALLY INVOLVE THE EXCHANGE OF A MUCH GREATER CHARGE
AND ARE USUALLY MORE DESTRUCTIVE.

THE GREATEST DANGER ASSOCIATED WITH THE POSITIVE FLASHES, HOWEVER, IS
THAT THEY STRIKE IN AREAS WHERE MOST PEOPLE THINK THEY ARE SAFE FROM
THE STORM. THEY GENERALLY STRIKE WELL BEYOND THE AREA WHERE RAIN IS
FALLING AND WELL BEYOND THE MAIN AREA WHERE MOST OF THE LIGHTNING,
NEGATIVE FLASHES, AND THUNDER IS OCCURRING. CONSEQUENTLY, MANY
VICTIMS ARE CAUGHT COMPLETELY OFF GUARD.

THE BEST ADVICE IN ORDER TO MINIMIZE YOUR RISK OF BECOMING A
LIGHTNING VICTIM IS TO GET TO A SAFE SHELTER SOONER AND TO STAY
THERE LONGER. IN GENERAL, IF YOU CAN HEAR THUNDER, YOU ARE WITHIN
STRIKING DISTANCE OF THE STORM.

HERE'S A LIST OF TOPICS THAT WILL BE COVERED WILL BE COVERED LATER
THIS WEEK.

WEDNESDAY - OUTDOOR SAFETY
THURSDAY - SAFE SHELTERS AND INDOOR SAFETY.
FRIDAY - THE FACTS ABOUT LIGHTNING STRIKE VICTIMS

FOR MORE INFORMATION ABOUT LIGHTNING SAFETY VISIT NOAA'S LIGHTNING
SAFETY WEBSITE AT WWW.LIGHTNINGSAFETY.NOAA.GOV

Local Climate Water & Weather Topics:
Current Hazards, Current Conditions, Radar, Satellite, Climate, Weather Safety, Contact Us

National Weather Service
Newport/Morehead City, NC Weather Forecast Office
533 Roberts Rd, Newport, NC 28570
(252) 223-5737
mhx.webmaster@noaa.gov
Page last modified: June 19, 2009
Disclaimer
Credits
Glossary
Privacy Policy
About Us
Career Opportunities