Sunday, June 5, 2011

Severe Thunderstorm Safety

There are typically almost 2,000 thunderstorms in progress around the world at any given time.  Only a small fraction (less than 1%) are classified as severe.  Severe thunderstorms are those that produce hail at least 1" in diameter (quarter-sized) and/or wind gusts of 58 mph or greater.

A small fraction of severe thunderstorms produce tornadoes, but all thunderstorms are capable of producing deadly lightning.  The frequency of lightning or amount or duration of rain have nothing to do with whether a thunderstorm is classified as "severe."  Severe thunderstorms can produce straight-line wind as strong as some tornadoes and can produce damage over a much wider area.

Severe thunderstorm and lightning safety rules include:
  • Find shelter immediately.  Go to a sturdy building that will withstand high wind.
  • Avoid electrical appliances and corded telephones.
  • If possible, bring your car inside a garage and secure loose objects.
  • Tune in to local broadcast information or another trusted source to listen for any updates, including the possible subsequent issuance of a Tornado Warning.  NOAA Weather Radio is the preferred source for all severe weather warnings.
  • Incorporate the 30/30 Rule during a lightning storm, whether it is severe or not. If the delay between lightning and a subsequent clap of thunder is less than 30 seconds, seek shelter, then wait 30 minutes after the last thunder to resume outdoor activities.
  • If on a boat, return to shore and seek shelter, at least in an enclosed metal vehicle.
  • If caught outdoors during a lightning storm, avoid being the highest point in the immediate area and avoid metallic objects, including non-enclosed vehicles (motorcycles, bicycles, golf carts, farm equipment). Avoid lone trees and the tallest trees, as they could be the object struck.
A Severe Thunderstorm Watch means that conditions are favorable for the development of severe thunderstorms, but none has been observed.  Keep an eye on the sky and listen for subsequent warnings.

A Severe Thunderstorm Warning means that a severe thunderstorm is occurring or imminent and has been detected by Doppler Radar or reported to the National Weather Service by a trained spotter or law enforcement agency in that area.  Exercise the safety tips above.

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

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