The 11 August 1999 Salt Lake City tornado

On 11 August 1999, an F2 tornado tore through downtown Salt Lake City, UT during the noon hour. Data were collected by both the National Weather Service WSR-88D radar (~40 nm from Salt Lake City) and the Federal Aviation Administration Terminal Doppler Weather Radar (TDWR; ~10 nm from Salt Lake City). The TDWR data were not available to the forecasters in real-time.

At their respective ranges from Salt Lake City, the WSR-88D and TDWR beam diameters are approximately 4300 feet and 500 feet, respectively. Also, the WSR-88D is 2300 feet higher than Salt Lake City while the TDWR, designed for low-level wind shear detection near airports, is at the same elevation as Salt Lake City.

Both radars showed that the tornado developed rapidly upward when an updraft formed over an area of weak rotation along a pre-existing boundary layer convergence line. However, the convergence line and rotation signatures were much more evident in the TDWR data. While the TDWR provided much higher resolution data at lower altitudes than the WSR-88D, neither radar provided significant warning lead-time owing to the sudden development of the tornado.