Intense Thunderstorms

Thunderstorms are usually intense, short-lived storms that produce high winds, hail, and heavy rainfall. These storms can be caused by convection in moist tropical air masses over continental surfaces or fast-moving cold fronts that displace those moist air masses (Hirschboeck, 1987). When these storms develop over mountainous areas where the precipitation is concentrated by the topography the potential for large, catastrophic floods is great (Hall, 1981). For example, see Figure 4. The eastern slope of the Rocky Mountains and the southwestern deserts of North America are

Figure 3 Water and sand washed inland to make travel difficult in North Topsail Island, North Carolina, after hurricane Fran. See ftp site for color image.

common locations for the development of thunderstorms. As moist air encounters higher elevations in these locations, it is forced to rise. Unstable atmospheric conditions are created as mountain slopes heat and in turn heat the atmosphere. Adiabatic cooling causes condensation and the development of large cumulonimbus clouds that can reach the upper altitudes of the troposphere. Sometimes there is iittle movement associated with a thunderstorm or thunderstorm complex, with respect to the ground; heavy precipitation concentrated in a small geographical area can have catastrophic results.

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