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Severe Weather

Some of the most feared and destructive events in life are due to severe weather, often in the form of hurricanes, tornadoes, thunderstorms, or a combination of these. Hurricanes are the single greatest natural threat to human life worldwide.

Hurricanes

Hurricanes (called typhoons in the western Pacific Ocean and cyclones in India) are lows, or cyclones, that form over oceans in the tropics. The period of June through November is called the "hurricane season," as almost all hurricanes form during these months, especially during August, September, and, October. At this time of the year the tropics receive a tremendous amount of energy from the sun, causing enormous amounts of ocean water to evaporate. Warm, moist air move in, forms above the surface of the ocean. Huge masses of colder, heavier air move in, forcing the warm, moist air upward creating violent, whirling movements of air that spiral toward the center of the storm. With winds speeds of 64 kilometers to 120 kilometers per hour.

Tornadoes

Tornadoes, also called funnel clouds or twisters, are the smallest, most violent, and most short-lived storms. When they occur almost exclusively in the United States. Although they can occur in any level land area, and all of the forty-eight contiguous states have experienced them, the region that seems most vulnerable to tornadoes beings at Texas and fans out to the east and north from that point through a path called the "tornado belt". Usually, cold, heavy air pushes its way under warm air masses. Sometimes, however, a layer of cold, dry air to pushed over a layer of warm, moist air. When this happens, the warm, moist air can quickly force its way up through the layer of cold air in a spiral fashion, forming a tornado. The tunnel of the tornado may or may not reach the ground, and sometimes it touches down at one point, lifts for a while, then touches down again a short distance away. It moves in a wandering path at speeds of about 40 to 64 kilometers per hour. The spinning winds in this powerful updraft can reach speeds up to 800 kilometers per hour.

Tornadoes are devastating to populated areas because they can sweep across the landscape without warning.

Thunderstorms

Cumulus clouds are usually fair-weather clouds, but they can respond to unstable atmospheric conditions, grow tall and dark, and become cumulonimbus clouds, or thunderheads. Thunderstorms come from cumulonimbus clouds, and they are accompanied by lightening, thunder, strong gusts of wind, heavy rain, and sometimes hail. Thunderstorms are associated with strong updrafts of warm, moist air and equally rapid downdrafts of cool air. Water accumulation in a thunderhead can reach 500,000 or more.

Some of the most severe occur when a single thunderstorm affects one location for an extended time.