SEVERE WEATHER VERIFICATION STATISTICS

Send Comments or Questions to:
Joe Dellicarpini, Storm Data/Storm Verification Program Leader
Joseph.Dellicarpini@noaa.gov

This section contains verification statistics for Severe Thunderstorm Warnings and Tornado Warnings issued by the National Weather Service in Taunton dating back to 1997.

In order to verify a warning, severe weather must occur in the warned county (or counties) during the time the warning is in effect. Reports are typically received from trained Skywarn spotters, amateur radio operators, and law enforcement agencies. In some cases, the media and the public provide severe weather reports.

Severe Thunderstorm Warnings are verified by reports of large hail, measured wind gusts of 58 mph or higher, or wind damage where gusts of 58 mph or higher are implied (i.e., large trees downed or branches downed that are 2" in diameter or greater).  This is not always the case however. Trees in saturated soils can be uprooted by lesser wind speeds. Large branches can break either because of dead wood, or because branches with leaves sometimes catch the wind like a sail. Nevertheless, in the protection of life and property, any wind damage is used as a severe weather event. A Tornado Warning can be verified by reports of a tornado, or by the criteria which verifies a Severe Thunderstorm Warning.

The numbers listed for each season are fairly easy to understand. Line A is the total number of Severe Thunderstorm Warnings and Tornado Warning issued, which are the types of warnings used in severe weather verification. Line B is the number of warnings issued that did not have a report of severe weather, and thus did not verify. Line C, Warned Severe Events, include the number of verified warnings plus multiple severe events within the same warning. A multiple severe event occurs when two or more reports are received from the same county during the time a warning is in effect. The reports must be at least 15 minutes apart, or from locations that are at least 10 miles away from each other. Line D is the number of severe weather events that occurred without a warning in effect (also called "missed events"). Line E, Total Severe Events, is the sum of Warned Severe Events and Missed Events.