Low-level winds in tornadoes and potential catastrophic tornado impacts in urban areas

Abstract

Using an axisymmetric model of tornado structure tightly constrained by high-resolution wind field measurements collected by Doppler on Wheels (DOW) mobile radars, the potential impacts of intense tornadoes crossing densely populated urban areas are evaluated. DOW radar measurements combined with in situ low-level wind measurements permit the quantification of low-level tornadic winds that would impact structures. Axisymmetric modeled wind fields from actual and hypothetical tornadoes are simulated to impact high-density residential and commercial districts of several major cities. U.S. census block data, satellite imagery, and other sources are used to characterize and count the number of structures impacted by intense winds, up to 132 m s-1, and estimate the level and cost of resulting damage. Census data are used to estimate residential occupancy and human casualties. Results indicate that a large and intense tornado crossing through residential portions of Chicago, Illinois, could result in tragic consequences with winds in excess of 76 m s-1 impacting 99 km2, substantially destroying up to 239,000 single-and dual-family housing units, occupied by up to 699,000 people, resulting in 4,500-45,000 deaths, and causing substantial damage to over 400,000 homes occupied by over 1,100,000 people. Widespread damage caused by winds exceeding 102 m s-1 could occur over a broad area of the high-rise office and apartment districts causing permanent structural damage to many such buildings. Smaller and less intense tornadoes would cause lesser, but still substantial, levels of damage and mortality. Tornadoes crossing Houston and Dallas-Fort Worth, Texas; New York, New York; Saint Louis, Missouri; Washington, D.C., and Atlanta, Georgia, could cause varying levels of damage and mortality. © 2007 American Meteorological Society.