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Monday’s Message – Severe Weather Awareness Week 2011

This week has been declared North Carolina’s Severe Weather Awareness week for 2011. Today we will define severe thunderstorms and learn why it is important to remember….When Thunder Roars, Go Indoors!

…Severe Thunderstorms…

In 2010 the National Weather Service redefined the hail criteria for severe thunderstorms. Hail stones must reach at least 1 inch in diameter, or the size of a quarter, to be classified as severe. The wind criteria for a severe thunderstorm is 58 mph or greater.

Over the last ten years there have been over 6000 reports of large hail and damaging wind statewide resulting in over thirteen million dollars in damage. Thunderstorms have also been responsible for a number of injuries and even deaths in the state resulting from lightning, high wind and tornadoes. The severe thunderstorm season in central North Carolina typically starts in March and does not end until late in the Fall. Some of the most damaging storms occur from March through early July.

In 2010 warnings issued by National Weather Service continued to provide an average of 19 minutes lead time for severe wind and hail, with a detection rate of ninety percent. The receipt of accurate and timely warnings is a vital part of any severe weather plan raising awareness when a significant threat is present. It is worth noting that the National Weather Service does not issue warnings for lightning. Given the deadly nature of lightning you should always be aware of the lightning danger anytime a thunderstorm is nearby. A good rule of thumb to live by: When Thunder Roars…Go Indoors.

…Large Hail…

In the last 5 years severe thunderstorms in North Carolina have produced severe damaging hail from the size of hen eggs to baseballs across the piedmont and eastern North Carolina. While hail is not usually life threatening, these large chunks of ice cause serious damage to roofs, siding, windows, automobiles, and crops. The large hail season in central North Carolina typically runs from March through early July, typically peaking in May.

Hailstones grow in thunderstorms with strong updrafts. These strong upward moving currents of air keep the ice suspended inside the thunderstorm, allowing the chunks of ice or hailstones to grow larger and larger. The longer hail stones remain suspended in the hail growth region of the storm, the larger they become. Thunderstorm updrafts that show signs of rotation on radar are very effective at suspending hail since the internal velocities in rotating updrafts are higher that those of non rotating updrafts. Once the hail stone becomes too heavy for the updrafts to keep suspended, it falls to earth. During the warmer summer months, hail stones melt considerably as they fall losing size and mass before hitting the ground. Therefore, we experience fewer large hail events from July through September.

…Damaging Wind…

Downburst Activity in Forsyth County

Severe gusts of wind from a thunderstorm called downbursts or straight line winds are a serious danger. Nationally, over the last 30 years, nearly as many people have been killed by straight winds as from tornadoes. Thunderstorm wind gusts rush down from the storm sometimes reaching speeds in excess of 100 mph. Thunderstorm winds of this magnitude affect large areas creating widespread damage and injuries from flying debris. Straight line winds can cause damage equivalent to that of a tornado.

Dangerous lines of well organized thunderstorms…called squall lines…occasionally move across central North Carolina in the spring and early summer. These dangerous storm systems can be very explosive racing across the state at over 50 mph creating widespread wind damage over large areas. Hiding from the severe wind when it strikes is similar to taking shelter during a tornado.

Damaging wind events in central North Carolina typically start in March lasting into September. Damaging thunderstorm wind events are most notable from May through early August which is much longer and later into the summer when compared to the hail threat.

…Safety…

You can protect yourself from thunderstorms by sheltering yourself from the wind and lightning. 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. Listen to a NOAA weather radio, television or local radio for the latest forecasts and possible threat of thunderstorms and severe weather. If warnings are issued…take action and protect your family and property. Being safe is a lot better than being sorry.

NC WAS #4 IN SEVERE WEATHER IN 2010

NWS Warning Criteria… http://www.erh.noaa.gov/rah/criteria/

PDF of Monday’s Message: Monday_2011

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