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Not All Thunderstorms Are Created Equal

Not All Thunderstorms Are Created Equal

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GREENVILLE, N.C. - Not all thunderstorms are created equal. Thunderstorms (or cumulonimbus clouds) are convective storms that form when warm, humid air rises in an atmosphere that is unstable. As long as the air this is being lifted is warmer than the air surrounding it, it will create clouds and convection; the warmer the air, the stronger the convection. The trigger to start this rising motion can be several things from unequal heating at the Earth's surface to a shallow boundary of converging winds (think the sea breeze that we often talk about). The most common is a frontal boundary (think cold front or warm front).  These fronts force the warm, humid air to rise.  There are two types of thunderstorms, an “ordinary “or “pulse” thunderstorm and a severe thunderstorm. Let's first talk about the ordinary thunderstorm.

ORDINARY THUNDERSTORM

An ordinary thunderstorm usually forms along a surface converging of winds. As humid air rises, it cools and condenses into a cumulus cloud or a cluster of cumulus clouds. As the clouds rises, the transformation of water vapor into a liquid and ice, it releases latent heat which keeps the air in the cloud warmer than the air around it (which makes it unstable).  

As the cloud grows larger and passes the freezing level in the atmosphere (32 degrees) the particles in the cloud grow larger. They become so heavy that the rising air can no longer support them and they begin to fall. While this process is takes place, drier air from outside the cloud is being drawn into the cloud and cools it. This cooler, drier air is heavy and begins to sink. This sinking air is called a downdraft. This could be enhanced if there is falling precipitation that drags the air down along with it. This is the cool breeze that you may feel in a thunderstorm.

The appearance of a downdraft marks the beginning of a mature thunderstorm. The updraft and downdraft in a thunderstorm constitute a “cell”. There could be several cells in one storm. During this mature stage, the storm grows and may reach the top of this layer of the atmosphere (called the Troposphere) where upper level winds spread the cloud out and it takes on the anvil shape.

These storms usually dissipate within 15 to 30 minutes after reaching the mature stage because the downdrafts usually tend to last longer and cut off the inflow of warm humid air that the storm needs to survive. (see pic 1)

SEVERE THUNDERSTORM

A severe thunderstorm, by definition, is any thunderstorms that produces hail at least one inch in diameter and/or wind gusts of 58 mph and/or produces a tornado. The longer the storm survives, the greater the likelihood of it becoming severe. Like ordinary thunderstorms, severe thunderstorms form as warm, moist air is forced to rise into the atmosphere. Severe thunderstorms, unlike ordinary thunderstorms, form with a strong vertical wind shear (the winds turn as you go higher into the atmosphere).

In severe thunderstorms, the updraft can become so powerful that the cloud is able to grow up to 60,000 feet (12 miles) into the next layer of the atmosphere (Stratosphere). The violent updrafts keep hailstones suspended in the cloud long enough for them to grow to considerable size until they get heavy enough to fall to the ground.  (see pic 3)

SUPERCELL THUNDERSTORM

A Supercell is a specific type of severe thunderstorm. If winds aloft become stronger than the winds at the surface and they change direction with height then they create wind shear. If this wind shear is strong enough then it can cause the whole storm to rotate. These storms can last up to an hour or longer. This type of storm is able to produce grapefruit sized hail, damaging surface winds from powerful downdrafts and long lasting tornadoes.

In eastern North Carolina, it is more common to see ordinary thunderstorms in the summer due to the sea breeze or instability due to the warm, moist air. In the spring is when it is more common to see severe thunderstorms and super cells due to the transition from a cold season to a hot season as the two air masses clash. Whatever the weather, your First Alert weather has you covered and will alert you to any dangerous weather. (see pic 2)

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