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Thunderstorm Definitions and Safety

According to the National Weather Service (NWS), a thunderstorm occurs when an observer hears thunder, Radar observers use the intensity of the radar echo to distinguish between rain showers and thunderstorms.  Lightning detection networks routinely track cloud-to-ground flashes, and therefore thunderstorms. Thunderstorms arise when clouds develop sufficient upward motion and are cold enough to provide the ingredients (ice and supercooled water) to generate and separate electrical charges within the cloud.  The cumulonimbus cloud is the perfect lightning and thunder factory, earning its nickname, "thunderhead."  

Thunderstorms are like nature's heat pumps. At the very top of giant thunderstorms, air temperatures can sometimes drop to below -100
EF.  On hot Wyoming summer afternoons, this air may originate near the ground at 100EF. Thunderstorms carry the sun's energy from the surface into the cooler reaches of the atmosphere.  Without this convective heat transport it is estimated that the mean temperature of the planet would increase by over 20EF, making many areas uninhabitable.

Important Definitions You Should Know:
Watch:  Conditions are favorable for the development of a severe weather event in or near the watch area.  Prepare for the possibility of severe weather. Warning:  A severe weather event is imminent of occurring in the warned area.  It is time to take action!  Put preparedness plans into action.

By definition, the National Weather Service classifies a thunderstorm as severe if it contains hail of three-quarter inches or larger, and/or wind gusts of 58 mph or higher, and/or a tornado.  Severe thunderstorm watches, meaning conditions are suitable for severe thunderstorm development during the next several hours, are issued for areas several hundred miles on a side by the NWS Storm Prediction Center in Norman, Oklahoma.   severe thunderstorm warning is issued by the local NWS office, usually for a county or several counties over an hour or so, based on spotter reports or radar indications of conditions exceeding severe levels. If there is a distinct threat or actual observation of a tornado, a tornado warning is issued.  Tornadic storms also produce hail, downbursts, and lightning, and those hazards should be likewise considered.

If a warning is issued for your area you need to move immediately to a substantial building or shelter.  Stay away from windows.  If a tornado warning is in effect move to the lowest floor of your home.  Go to an interior room (such as a closet or bathroom) and cover your head and body.

Tornado Spotters Cartoon Are you interested in helping the NWS in Riverton fulfill its mission of protecting lives and property across western and central Wyoming?  Check out our spotter training schedule and join the team.  Reports from certified spotters can be of immense help in making warning decisions.  These spotters are also eligible to participate in as an eSpotter

Learn more by clicking on one of the topics listed below.

Wind Lightning
Flash Floods Tornadoes
Hail Thunderstorms

Back to Thunderstorms and Associated Weather Phenomena.


Martner, Brooks E. Wyoming Climate Atlas, University of Nebraska Press 1986. 
Lyons, Walter A. Ph.D.  The Handy Weather Answer Book,Visible Ink Press, 1997

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