To complement the Daily Summary for Tuesday, 20 April 1999
SEVERE LOCAL STORM TERMINOLOGY
The following list includes terminology used by the National Weather
Service for those public statements pertaining specifically to
severe local storms. These storms are usually convective and contain
severe weather with large hail (3/4 inch diameter
or larger) and/or strong winds (58 miles per hour or greater)
meeting the specific criteria, as well as tornadoes and flash
flooding due to excessive precipitation in thunderstorms. A description
of those statements used to alert the public for flash floods
will accompany Thursday's concept. The other pertinent terms are
given:
- Severe thunderstorm watch -- Issued by the Storm Prediction
Center in Norman, OK to alert the public that conditions are favorable
for development of thunderstorms meeting any of the criteria of
large hail (3/4 inch diameter or larger) and/or strong winds (58
miles per hour or greater) in or close to the watch area. Watches
typically are in effect for several hours.
- Severe thunderstorm warning -- Issued by the local
National Weather Service Office to warn the public that a thunderstorm
producing 3/4 inch (1.9 centimeters) or larger diameter hail and/or
winds equal to 58 miles per hour or greater is occurring. The
warning indicates where the severe thunderstorm has been located,
what communities are to be affected and the primary threats to
public safety that are associated with the storm. Persons in the
affected area should take immediate action.
- Tornado watch -- Issued by the Storm Prediction Center
to alert the public that conditions are favorable for the development
of tornadoes in and close to the watch area, which is delineated
in the tornado watch statement. These watches are issued with
information concerning the watch area and the length of time they
are in effect; watches are usually in effect for several hours.
- Tornado warning -- Issued by the local National Weather
Service Office to warn the public that a tornado has been sighted
by storm spotters or has been indicated by radar. These warnings
are issued with information concerning where the tornado is presently
located and what communities are in the anticipated path of the
tornado. The public is expected to heed these warnings and take
appropriate action.
The Storm Prediction Center issues Convective Outlooks
and Second Day Severe Weather Outlooks that are primarily
for internal use and outline the geographic regions where severe
weather may develop. However, some of the information contained
in these guidance products are used on television weathercasts.
These Outlooks include levels of risk.
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological Society.