Severe Weather Safety Information

Even without a tornado, a severe thunderstorm can be a damaging and life threatening event. Deaths and injuries occasionally occur from strong thunderstorm winds. Thunderstorms also accounted for millions of dollars in property damage. Also large hail can be responsible for tremendous property damage.

The National Weather Service defines a thunderstorm as "SEVERE" when wind speeds reach 58 mph or stronger and/or hail is produced that is 3/4 inch in diameter or larger and/or a tornado is produced.

Downward rushing currents of air, or downdrafts, occur along the leading edge of almost all thunderstorms and along the trailing edge as well, in some cases. This process, the same that can bring a welcome cooling breeze on a hot summer day, can also produce winds as damaging as those of a tornado. Strong localized downdrafts are called "downbursts", These intense concentrations of sinking air fan out upon striking the earth's surface and produce damaging winds. They may be accompanied by a "roaring sound". Thunderstorms that produce downbursts typically produce several in succession of various sizes and intensities. There may be a well defined damage path similar to that of a tornado or concentrated damage may occur in one spot.

Downdraft winds from thunderstorms often reach destructive force in Mississippi. These damaging winds area called "straight-line winds", and can have winds speeds up to 60 mph...and can even reach or exceed 100 mph on occasion. What makes these winds so damaging is the rapid increase in local wind speeds when downbursts strike. Winds that rapidly jump from 10 to 60 mph can produce more damage than sustained 60 mph wind. Frequently, damage that is attributed to tornadoes is actually due to the straight-line winds of a downburst. In Mississippi the frequent occurence of downburst winds makes it imperative that the threat of non-tornadic severe thunderstorms be taken seriously as severe thunderstorms with tornadoes.

Large hailstones can develop within strong thunderstorm updrafts. The stronger the updraft is, the larger the stones that can be held up in the updraft without falling to the ground. Severe thunderstorm in Mississippi usually produce hailstones one inch in diameter or smaller. A few of the storms produce golfball to baseball size hailstones which cause substantial damage. The most severe thunderstorm across the country have been known to produce up to grapefruit size hailstones.

The potential for deaths, injuries, and damage from severe thunderstorms makes it imperative that our preparedness plans include thunderstorm safety and that we heed Severe Thunderstorm Warnings.

Just like Tornado Watches or Tornado Warnings, watches and warnings are issued for areas threatened by severe thunderstorms.

SEVERE THUNDERSTORM WATCH: conditions are favorable for severe thunderstorms to develop in or close to the watch area. Be ready to seek shelter if a storm approaches or a warning is issued for your area.

SEVERE THUNDERSTORM WARNING: a severe thunderstorm is indicated by radar, or reported by a reliable source. Move to a safe place immediately and stay away from windows.

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