Fredericktown, Ohio

... This public information statement is in conjunction with
severe weather awareness week...

... Severe thunderstorms...

It has been estimated that at any given moment nearly 2000
thunderstorms are in progress over the surface of the Earth.
There are at least 100000 thunderstorms per year across the
United States.

Thunderstorms are relatively small when compared to hurricanes
and winter storms. However... despite their size... all thunderstorms
are dangerous. Every thunderstorm produces lightning... which
kills more people each year than tornadoes. Heavy rains from
thunderstorms can lead to flash flooding. Strong winds... hail... and
tornadoes are also dangers associated with thunderstorms.

About 10 percent of the estimated 100000 thunderstorms that occur
across the U.S. Are classified as severe. Your National Weather
Service considers a thunderstorm severe if it produces hail three
quarters of an inch or greater... winds of 58 mph or greater... or
tornadoes. In northwestern Pennsylvania ... you can expect about 30 to
50 days a year in which there will be a thunderstorm.

Thunderstorms are most likely in the warmer months and also are
most common in the later afternoon and evening. However... they
can occur during anytime of year and anytime of day.

While we bask in 90 degree plus heat on a hot sweltering Summer
day... a blizzard is raging at the top of the thunderstorm. Once ice
crystals form... the particles can get very efficient at separating
electrical charge (just as you do when you walk across a new
carpet and then touch a metal object). When the charge builds up
enough... a lightning stroke occurs. An intense flash which can heat
a small corridor of air to 50000 degrees fahrenheit. Thunder is the
sound produced by the explosive expansion of this heated air. When
lightning is close by... the thunder sounds like a sharp crack.
Distant strokes produce growling and rumbling noises.

Dangers associated with thunderstorms:
... Lightning...
-occurs with all thunderstorms
-kills almost 100 people and injures nearly 300 each year
-causes several hundred million dollars in damage annually
... Flash floods...
-the number "one" thunderstorm killer
-most deaths from flash floods are from people getting trapped in
cars
... Straight-line winds...
-responsible for most thunderstorm wind damage
-winds can exceed 100 mph
-the downburst (a type of straight-line wind) can cause damage
equivalent to a strong tornado and can be extremely dangerous to
aviation
... Large hail...
-causes nearly $1 billion in damage to property and crops annually
-costliest hail storm in the U.S. Occurred in Denver on 11 July 1990.
The total damage estimate was $625 million
... Tornadoes...
-natures most violent storms
-winds can exceed 200 mph

Gary Garnet
warning and coordination meteorologist... NWS Cleveland