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Severe Weather

SEVERE WEATHER TERMS AND DEFINITIONS (Return to top)

Warning: A particular weather hazard is either imminent or has been reported. A warning indicates the need to take immediate action to protect life and property. The type of hazard is reflected in the type of warning (e.g., tornado warning, blizzard warning).

Watch: A particular hazard is possible, or when conditions support its occurrence. A watch is a recommendation for planning, preparation, and increased awareness (i.e., to be alert for changing weather, listen for further information, and think about what to do if the danger materializes).

Tornado: A violently rotating column of air in contact with the ground and extending from the base of a thunderstorm.

Severe Thunderstorm: A thunderstorm that produces tornadoes, hail 0.75 inches or more in diameter, or winds of 50 knots (58 mph) or more.

Straight-line Winds: Generally, any wind that is not associated with rotation, used mainly to differentiate them from tornadic winds.

Flood: The condition that occurs when water overflows the natural or artificial confines of a stream or other body of water, or accumulates by drainage over low-lying areas.

Flash Flood: A flood that rises and falls quite rapidly, usually as the result of intense rainfall over a relatively small area. Usually it occurs within 6 hours of a rain event.

Supercell: A thunderstorm with a persistent rotating updraft. Supercells are rare, but are responsible for a remarkably high percentage of severe weather events - especially tornadoes, extremely large hail and damaging straight-line winds.

Squall Line: A solid or nearly solid line or band of active thunderstorms.

Downburst: A strong downdraft resulting in an outward burst of damaging winds on or near the ground. Downburst winds can produce damage similar to a strong tornado. Although usually associated with thunderstorms, downbursts can occur with showers too weak to produce thunder.

Funnel Cloud: A condensation funnel extending from the base of a towering cumulus or cumulonimbus cloud, associated with a rotating column of air that is not in contact with the ground (and hence different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if either a) it is in contact with the ground or b) a debris cloud or dust whirl is visible beneath it.

TORNADO SAFETY (Return to top)

In homes or small buildings: Go to the basement (if available) or to an interior room on the lowest floor, such as a closet or bathroom. Wrap yourself in overcoats or blankets to protect yourself from flying debris.

In schools, hospitals, factories or shopping centers: Go to interior rooms and halls on the lowest floor. Stay away from glass enclosed places or areas with wide-span roofs such as auditoriums and warehouses. Crouch down and cover your head.

In high-rise buildings: Go to interior small rooms or halls. Stay away from exterior walls or glassy areas.

In cars or mobile homes: ABANDON THEM IMMEDIATELY! Most deaths occur in cars and mobile homes. If you are in either of those locations, leave them and go to a substantial structure or designated tornado shelter.

If no suitable structure is nearby: Lie flat in the nearest ditch or depression and use your hands to cover your head.

LIGHTNING SAFETY (Return to top)

All thunderstorms produce lightning and are dangerous. Lightning kills more people each year than tornadoes. Lightning often strikes as far as 10 miles away from any rainfall.

Many deaths from lightning occur ahead of the storm because people try and wait to the last minute before seeking shelter. You are in danger from lightning if you can hear thunder. If you can hear thunder, lightning is close enough that it could strike your location at any moment. Get inside!

Lightning injuries can lead to permanent disabilities or death. On average, 10% of strike victims die; 70% of survivors suffer serious long term effects.

Blue Skies and Lightning: Lightning can travel sideways for up to 10 miles. Even when the sky looks blue and clear, be cautious. If you hear thunder, take cover. At least 10% of lightning occurs without visible clouds overhead in the sky.

HEAT SAFETY (Return to top)

How can you be prepared and stay safe?

WEATHER RADIOS (Return to top)

NOAA Weather Radio All Hazards (NWR) is a nationwide network of radio stations broadcasting continuous weather information directly from the nearest National Weather Service office. NWR broadcasts official Weather Service warnings, watches, forecasts and other hazard information 24 hours a day, 7 days a week.

These radios may be purchased at any major department store and many other locations.