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What Causes Thunderstorms

March 23, 2012 by · Comments Off on What Causes Thunderstorms 

What Causes Thunderstorms, Thunderstorms form when an air mass becomes so unstable that it overturns (convects) violently. “Unstable” means that the air in the lowest layers is unusually warm and humid, or that the upper layers are unusually cool, or oftentimes, both.

Pockets of rising near-surface air in an unstable air mass expand and cool, and as some of the water vapor present condenses into a cloud it releases heat, which then makes the air parcel even warmer, forcing it to rise still higher in the atmosphere.

If the lower level air is sufficiently warm and humid, and the higher altitude air is sufficiently cool, this process continues until a tall convective cloud — the thunderstorm — is formed. The result can be a storm extending as high as 40,000 to 60,000 feet (8 to 12 miles). The upper portions of the storm — even in the warm tropics — are made of ice: ice crystals, graupel, snow, and sometimes hail. About 50% of the rain reaching the surface in a thunderstorm originated as ice in the upper reaches of the storm.

The updrafts in thunderstorms can be very strong — 50 knots or more — which can help support the weight of hailstones as they grow. Such updrafts cause extreme turbulence for aircraft, which will only fly through the strongest portions of thunderstorms if the pilots have no other choice. Despite the large stresses this puts on planes (and their passengers), modern jet aircraft are designed to withstand those stresses.

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