Hazard Vulnerability Assessment

Severe Thunderstorms

General information index. Also see Current Hazard Mitigation.

Alexander County has experienced an average of 27 severe thunderstorms per year. Many hazardous weather events are associated with thunderstorms. Fortunately, the area affected by any one of them is fairly small and—most of the time—the damage is fairly light. Lightning is responsible for many fires each year, as well as causing deaths when people are struck. Under the right conditions, rainfall from thunderstorms causes flash flooding. Hail up to the size of softballs damages cars and windows, and kills wildlife caught out in the open. Strong (up to more than 120 mph) straight-line winds associated with thunderstorms knock down trees and power lines. Straight-line winds are often thought to be tornados because of their often violent destruction. Tornados (with winds up to about 300 mph) can destroy all but the best-built man-made structures. Therefore the number of thunderstorms and the potential for a variety of other weather events makes this hazard one of the most potentially devastating.

To a limited degree, potential thunderstorm development is predictable, as is the possible track of storms likely to produce severe thunderstorms, or as depicted, super-cell thunderstorms. Generally these storms develop south west of Alexander County and travel north east. Thunderstorm watches and warnings are issued by the National Weather Service in Greenville/Spartanburg, SC. While super-cell storms are very rare, they are possible. It is also possible that a super-cell or other severe thunderstorm can develop and strike any facility, business or residential area. The entire county, including the municipalities are vulnerable, as is the entire population. Reasonable expectation, however would be for storms of considerably less intensity, resulting in a considerable reduction in the calculations below. This assessment assumes multiple severe thunderstorms producing at least one super-cell producing straight line winds of maximum magnitude of 120 miles per hour. It should be noted that these damages are approximate to an F2 tornado.

A super cell thunderstorm with rotating updraft makes a perfect backdrop for a mobile mesonet during the STEPS project. Photo by Daphne Zaras, NSSL. National Oceanic & Atmospheric Administration (NOAA)

Table TS1

** Estimated / Potential Economic Impact from a catastrophic wind event

The potential for debris generation is provide below as information for planners, solid waste professionals and county executives as a planning tool for the need for possible landfill space. Debris management following a major wind event is a costly and time consuming portion of disaster recovery. Costs are associated with debris and efforts to reduce the amount of debris that would be stored in a landfill may become a mitigation measure for the future.

Table TS2

*** Estimated / Potential Debris generated from a severe thunderstorm which generates a F2 tornado.

**** Potential Death and injury totals in a severe thunderstorm

*Source - NC Department of Commerce Economic Development Information System
** HAZUS Information Data base - FEMA - Dunn and Bradstreet 1994. Adjusted to 2002 by 31%. Worst case scenario.
*** Debris management program mathematical formulas - FEMA- NCDEM- GCEM- 1999
**** Based on historical information 1950 - 2000 - Tornado Project Online (www.tornadoproject.com)