Tuesday, February 21, 2012

Severe weather awareness week: LIGHTNING

One of the most deadly of all weather phenomena is lightning. Lighting is basically a large spark of static electricity within the clouds or between the cloud and the Earth. Over the past 30 years lightning has killed an average of 55 people per year but that number continues to drop thanks to educating the public on lightning safety. In fact, last year had the lowest amount of lightning deaths on record with 26.

As a thunderstorm develops, air inside the storm moves up and down in the form of updrafts and downdrafts. Inside the currents of air are ice particles, whether small ice crystals or large hailstones. These ice crystals will collide with each other causing a buildup of static electricity, much like what happen when you rub your feet across the floor only to get shocked by the door knob as you reach for it. The thunderstorm is doing the same thing. As the ice particles continue to collide in the storm, some become positively charged and some become negatively charged. The positive charged ice crystals will move towards the top of the thunderstorm while the negative charged ice crystals will settle across the bottom or mid level of the storm. As the storm moves over the ground the surface charge becomes positive. Once the difference becomes great enough a discharge of static electricity will occur just like the shock that comes off your finger as you reach for the door knob. Only in this case the shock is a bolt of lightning that can reach a temperature of 50,000°F. As the air heats around the lightning bolt it will expend very rapidly causing a loud boom or thunder.

In some cases the positive charge at the top of the storm can become so great that a large lightning bolt will race from the top of the cloud towards the ground well out ahead of the storm. This is called positive lightning and occurs because the ground well ahead of the storm has not yet become positively charged. In some cases this lightning bolt can hit up to ten miles away from the storm. This is the most dangerous type of lightning as many times it will strike when you don’t know a storm is near you due to the lack of clouds and it usually has the strongest amount of electric current.

So next time you hear thunder it is time to move indoors. For every five seconds you can count between lightning and its thunder is a distance of 5 miles. So even the faintest sound of thunder means it is close enough to strike. Also, it is a great idea to wait 30 minutes after the last sound of thunder to make sure the storm has passed to a safe distance.

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