The National Weather Service (NWS) has defined a severe thunderstorm as one that produces:
1 - Hail, 3/4" in diameter or larger (dime to penny size)
2 - Wind at or above 58 m.p.h. (50 knots); and / or
3 - A tornado
When attempting to verify a warning, the NWS looks for these occurrences, in addition to other events that imply a severe thunderstorm, such as significant damage.
Use of the following criteria when determining whether you are dealing with an actual severe weather event.
Remember, your severe weather reports are vital to the NWS, hours or even days after the event has
Include the time and exact location of the event when reporting.
THE FOLLOWING SHOULD BE CONSIDERED TO BE SEVERE EVENTS AND
REPORTED AS SOON AS POSSIBLE:
A credible report of a tornado on the ground. If the funnel extends 1/2 way or more from the base of the cloud to the ground, or if dirt / debris are seen on the ground underneath the funnel, it should be reported as a tornado.
1 - Measured thunderstorm wind gusts of 58 m.p.h. (50 knots) or more
2 - Estimated thunderstorm wind gusts of 58 m.p.h. (50 knots) or more from a certified spotter
3 - Trees blown down or uprooted (more than 1-2)
4 - Large tree limbs or branches blown down (more than 1-2)
5 - Power lines blown down
6 - Permanent signs blown down (billboards, etc.)
7 - Roof damage from the wind (large area of roofing material removed)
8 - Windows broken by the wind
9 - Radio towers or large antennas blown down
10 - Home t.v. antennas blown down (more than 1-2)
11 - Campers heavily damaged or destroyed
12 - Mobile homes damaged by the wind
1 - Hail 3/4" in diameter or larger (dime or penny size)
2 - Windows or windshields broken by hail
3 - Roofs or house siding damaged by hail