Heat and Thunderstorms
By Erica Campbell on June 22, 2012, 3:24pm
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With the extreme heat of the past few days, eventually, Mother Nature has to release some energy. A cooling front, after extreme heat, is always a welcome occurrence. Unfortunately, this relief could mean thunderstorms…some reaching severe levels. To give a little background, a thunderstorm is a rain shower during which you hear thunder. Thunder is the sound given off by the rapid heating of the air due to lightning and all thunderstorms have lightning. A thunderstorm is classified as "severe" when it contains one or more of the following: hail which is one inch or greater, winds gusting in excess of 57 mph and rarely (but possibly), a tornado.
Around the world, there are an estimated 16 million thunderstorms each year. At any given moment, there are roughly 2,000 thunderstorms in progress around the world. There are about 100,000 thunderstorms each year in the U.S. alone. About 10% of these reach severe levels.
Three basic ingredients are required for a thunderstorm to form: moisture, rising unstable air, and a lifting mechanism to provide the "nudge." The sun heats the surface of the earth, which warms the air above it. If this warm surface air is forced to rise, it will continue to rise as long as it weighs less and stays warmer than the air around it. As the air rises, it transfers heat from the surface of the earth to the upper levels of the atmosphere. When the water vapor it contains begins to cool, releasing the heat, it condenses into a cloud. This cloud will eventually grow upward into areas where the temperature is below freezing. The more water vapor and the more “lift” the cloud has, the higher the cloud will build, The higher up into the atmosphere the cloud rises, the stronger the storm. Some of the water vapor turns to ice and some of it turns into water droplets. Both have electrical charges. Ice particles usually have positive charges, and rain droplets usually have negative charges. When the charges build up enough, they are discharged in a bolt of lightning…the sound waves the lightning causes are what we hear as thunder.
Because thunderstorms need the “triggers” moisture, rising unstable air and a “lift,” they love the hot, humid days of summer. This is one of the best ways to destabilize the atmosphere and provide thunderstorms the “fuel” that they need.
Thunderstorms have three basic stages: developing, mature and dissipating. The developing stage of a thunderstorm is a cumulus cloud being pushed upward by a rising column of air (updraft). The cumulus cloud soon looks like a tower, as the updraft continues to develop. There is little to no rain during this stage but occasional lightning.
The mature stage is when the updraft continues to feed the storm, but precipitation begins to fall out of the storm, and a downdraft begins (air pushing downward). When the downdraft and rain-cooled air spreads out along the ground, it forms a line of gusty winds (called a gust front). The mature stage is the most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes. The storm could sometimes have a black or dark green appearance.
Eventually, a large amount of precipitation is produced and the updraft is overcome by the downdraft beginning the dissipating stage. At the ground, the gust front moves out a long distance from the storm and cuts off the warm moist air that was feeding the thunderstorm. A typical thunderstorm can last 20-30 minutes, depending on the severity.
Yes, the cooling down of a cold front is a welcome relief from all of this recent heat. But when temperatures increase, along with the humidity, keep an eye to the sky. Mother Nature might just have a show to put on first.
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