On The Job - Salt Lake City: Training For Disasters Pays Off When Tornado Rips Downtown Areas

Before Aug. 11, 1999, the last time a tornado passed through Salt Lake City, the Green Bay Packers beat the Oakland Raiders in Super Bowl II, Warsaw Pact troops invaded what was then Czechoslovakia and North Vietnamese troops launched the Tet offensive. The year was 1968, and a weak tornado - rated at F0 on the Fujita scale with winds estimated at less than 65 mph - broke a few windows and was gone before most people even knew it had been there.

The twister that unexpectedly roared through downtown Salt Lake City last summer, though, was the "real deal." Rated at F2, it took a startled and frightened public by complete surprise. Potentially lethal winds of up to 165 mph immediately got everybody's attention as the twister wound its capricious way through a crowded downtown area.

When it finally dissipated after having touched ground for nine minutes, its 21/2-mile-long-by-half-mile-wide damage track left one person dead and 84 injured, 34 homes destroyed, 87 homes damaged and 20,000 customers in the downtown area without electrical power. Lightning also struck several people.

Salt Lake City, with a base population of 180,000, is the largest city in Utah. Commuters raise the total number of inhabitants to 350,000 during the day. The city is protected by a 346-member fire department, 270 of whom are engaged in suppression. The department responds out of 13 stations strategically situated over an area of 100 square miles.

Tornados are rare in Utah, which has experienced about 30 of them in 25 years; most of them touch down in sparsely populated areas and often are mistaken for dust devils. The topographical environment in Utah is not favorable to the formation of twisters. In order to form, tornados need a clash of air masses. Cold air from the north encounters warm air from the south and create the shear necessary for a tornado to form. The mountain ranges that are prevalent in Utah and other western states shred air masses and tear up systems.

The Utah Landscape

Interstate Highway 15 accesses the city from the south and north, Interstate 80 comes from a diagonally east-by-northeast direction and splits in two to form Interstate 215, essentially a huge loop road called the Belt Route around the city. Interstate 215 continues north and runs parallel to Interstate 15, giving access from that direction.Salt Lake City's streets, boulevards and avenues have been assigned both directional and numerical values and are primarily laid out in a grid system.

The Great Salt Lake Desert that stretches unabated to the Nevada border lies directly west of the city. Huge sun-scorched sand tracts characterize this vast, inhospitable area interspersed by rugged mountain ranges. It is uninhabited by humans save for a few tiny settlements and military firing ranges and testing grounds that are restricted areas.

Results of tornadic activity can be predicted. F1 denotes moderate damage, F3 means extreme damage and so on. Damage can also be reduced to an extent, if there is sufficient warning that a twister is on its way. Salt Lake City had none.

On Aug. 11, the National Weather Service's NEXRAD radar on Promontory Point, 45 miles northwest of Salt Lake City, initially detected a small rotation over the city's airport. Such cyclonic air circulation is often associated with strong thunderstorms, but rarely produces tornadoes.

The radar sits 6,500 feet above sea level and rotates like a lighthouse beacon. Its waves bounce off dust, moisture, rain, snow, haze, and even insects and birds to detect wind speeds, precipitation and storm structures that can produce tornadoes.