Jefferson, TX

... Continuing severe weather awareness week in Louisiana...

... This afternoons topics are damaging winds and hail...

Louisiana is affected by thousands of thunderstorms every year. The
strongest and most dangerous of these thunderstorms are defined as
severe thunderstorms. Severe thunderstorms are thunderstorms which
produce damaging winds... large hail and tornadoes. A thunderstorm
is severe when it produces winds of at least 58 mph... hail 1 inch
in diameter or larger... or a tornado. Severe thunderstorms can
occur during any time of the year in our four state region... but
are most common during the Spring and autumn months.

Thunderstorms are capable of producing very strong winds... but it is
important to remember that not all damaging thunderstorm winds are
caused by a tornado. Straight line winds refer to winds that are not
associated with rotating winds in a tornado. Rather... they move
forward along the ground in unidirectional fashion.

One form of straight line winds... the downburst... is a strong
downdraft of air that accelerates toward the ground in a
thunderstorm. Once near the ground... the downdraft can no longer
descend and therefore radiates outward in all directions... producing
a sudden rush of damaging winds at the surface. Two types of
downbursts exist... the microburst and the macroburst. The microburst
is a short lived event and of great concern to the aviation
community. It produces strong winds in an area less than 2.5 miles in
diameter. In contrast... macrobursts are longer lived and capable of
producing extensive wind damage across areas several miles in
diameter.

Straight line thunderstorm winds occasionally reach speeds in excess
of 100 mph. These winds may be intense enough to uproot trees and
produce substantial damage... if not complete destruction... to
buildings. If these winds occur in conjunction with large hail... the
damage will likely be even more extensive.

Hail that is 1 inch in diameter (as big around as a quarter) or
larger is considered severe. Hail is defined as precipitation in the
form of lumps or chunks of ice that develop inside stronger
thunderstorms. Hailstones are usually Oval shaped or round... but can
be also be spiky in appearance. Hail can range in size from pea
size... to greater than softball size. The largest hailstone on record
in the United States fell at Aurora... Nebraska on June 22... 2003.
This massive stone measured 18.75 inches in circumference... and over
7 inches in diameter.

Hail falls to Earth at speeds approaching 100 mph and can cause
immense damage to buildings... automobiles and vegetation. Annually...
hail storms cause more than one billion dollars in damage across the
entire United States. No part of the four state region is immune to
the dangers of large hail. Although being struck by hail is rarely
fatal... several dozen people are seriously injured each year in
hailstorms.

To protect yourself and your property from damaging winds and hail
associated with a thunderstorm... it is important to stay abreast of
the latest weather conditions. Staying updated through NOAA Weather
Radio from the National Weather Service... as well as monitoring
television... radio and the internet... will help you be better
prepared for the dangers associated with any severe thunderstorms in
your area.

Treat straight line wind events the same as you would an approaching
tornado. Seek shelter in a reinforced building... preferably on the
lowest floor... in an interior room or closet and away from any
windows. Always cover your head to protect against the impact of
flying debris. If you encounter hail while driving... turn around. You
may be driving into the core of a thunderstorm... which is where
tornadoes form. Report hail or wind damage to law enforcement as soon
as it is safe to do so and seek an alternate Route.

The National Weather Service would like to thank everyone involved in
making severe weather awareness week a Success.

&&

For more details on some of the significant severe weather events
across the four state region dating back to the 1978 Shreveport F4
tornado... please visit... www.Srh.NOAA.Gov/shv/events/