Emergency Plan - Grand Strand Water and Sewer Authority

EVENT SPECIFIC GUIDELINES 4 (ESG-4)
SEVERE THUNDERSTORM
Severe Thunderstorm
3.2.10. SITUATION
NOAA’s National Severe Storms Laboratory defines a severe
thunderstorm as having either tornadoes, gusts at least 58 mph, or
hail at least 3/4 inch in diameter
GSWSA and its service area are susceptible to the threat of severe thunderstorms.
In addition to tornadoes, which severe thunderstorms can produce (refer to ESG-2),
the other hazards of these storms are lightning, strong winds, flash flooding, and
hail.
Lightning causes an average of 80 fatalities and 300 injuries each year across the
nation. Lightning is involved with each and every one of the approximately 100,000
thunderstorms that occur each year in the United States. About 10% of these, or
10,000 storms, are classified as “Severe.”
Winds associated with a severe thunderstorm can exceed 100 mph and cause
damage equal to a tornado. This straight-line wind is called a downburst or
microburst, and comes from fast-moving air coming down out of a storm and
striking the ground.
Flash Flooding is the leading cause of death associated with thunderstorms,
averaging more than 140 fatalities per year. This hazard is minimized in the “flatland”
of our region, but is still a potential threat under certain conditions.
Hail causes more than $1 billion in property damage each year.
In our region, thunderstorms typically occur during the warm summer months,
fueled by the heating of the air that occurs. At any given moment around the world,
there are approximately 1,800 thunderstorms in progress, totaling more than 16
million per year.
3.2.11. THREAT or HAZARD INFORMATION
Thunderstorm: A storm that produces lightning, generally involving heavy rain.
Severe Thunderstorm: A thunderstorm that produces a tornado, hail at least ¾ inch
in diameter, or winds of 58 mph or stronger.
Severe Thunderstorm Watch: Issued by the National Weather Service when
conditions are favorable for the formation of severe thunderstorms. Indicates these
storms could form.
Grand Strand Water & Sewer Authority 107 CONFIDENTIAL MATERIALS
Emergency Management Plan
SECURITY SENSITIVE
June 7, 2013
NOT FOR PUBLIC
DISCLOSURE