03/14/06 — Tornado drill Wednesday: State marks severe weather week

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Tornado drill Wednesday: State marks severe weather week

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Published in News on March 14, 2006 1:47 PM

By Jeff Orrock

National Weather Service, Raleigh

RALEIGH -- A common threat in North Carolina is severe thunderstorms that can cause millions of dollars in damage every year. These powerful thunderstorms result in injuries and sometimes deaths. Most thunderstorm damage in the state is the result of strong winds and large hail. The severe thunderstorm season in central North Carolina typically starts in mid- to late March and continues until the middle of summer.

SEVERE WEATHER ...The National Weather Service considers a thunderstorm severe if it produces hail at least the size of a penny and or wind of 58 mph or greater. These minimum wind and hail parameters are the National Weather Service's warning criteria for severe thunderstorms.

LARGE HAIL ... In the past several years, severe thunderstorms in North Carolina have produced hail as large as tennis balls and even baseballs.

In the last 10 years there have been over 1,000 reports of hail at least 1 inch in diameter. Hailstones the size of baseballs fell in Rural Hall just north of Winston- Salem last year. Hail stones this size fall to the ground at nearly 200 mph. While hail is not usually life-threatening, these large chucks of ice, when driven by strong winds, cause serious damage to roofs, automobiles, and crops. Hail season in central North Carolina typically runs from mid-March through July, typically peaking in May.

Hailstones grow in thunderstorms with strong updrafts. These strong upward moving currents of air keep the hail suspended inside the thunderstorm, allowing the chunk of ice to grow larger and larger.

Once hail stones become too heavy for the updrafts to suspend them, they fall to earth as hail. Thunderstorm updrafts which show signs of rotation on radar are rather effective at suspending hail since the internal velocities in rotating updrafts are higher that those of non-rotating updrafts.

DAMAGING WINDS ...Strong gusts of wind from a thunderstorm, called downbursts or straight line winds, are another serious danger. These gusts of wind rush down from the sky and can reach speed in excess of 100 mph. Thunderstorm winds of this magnitude can impact large areas creating widespread damage. Damaging straight line wind can even cause damage equivalent to that of a tornado.

Lines of well-organized thunderstorms, called squall lines, also move across Central North Carolina in the spring and early summer. These dangerous storm systems can be very explosive and race across the state at over 50 mph creating widespread wind damage.

Damaging wind events in Central North Carolina typically start as early as mid-March and run into August. Damaging thunderstorm wind events are most notable from May through early August which is much longer than the typical severe hail season.

SAFETY ... You can protect yourself by hiding from the wind. Stay away from windows when storms approach and seek shelter in an interior bathroom or closet when the wind really starts to blow. Your best line of defense against severe thunderstorms is to stay informed. Watch for weather forecasts in newspapers and monitor broadcasts on NOAA weather radio, television or local radio stations for alerts and warnings. If warnings are issued, take action and protect your family and property. Remember, being safe is a lot better than being sorry.