Tornadogenesis and operational considerations of the 11 August 1999 Salt Lake City tornado as seen from two different Doppler radars

On 11 August 1999 a climatologically rare F2 tornado developed just west of downtown Salt Lake City, Utah (SLC), and moved directly through the city d uring the noon hour. Tornadogenesis was observed from a mountaintop WSR-88D Doppler radar 76 km (41 n mi) to the northwest of and 0.7 km (2300 ft) abo ve SLC and also from a Terminal Doppler Weather Radar (TDWR) located only 2 2.2 km (12 n mi) north of and at the same elevation as SLC. Data from the T DWR offer an unambiguous view of the development of a nondescending tornado as an intensifying updraft became juxtaposed over enhanced cyclonic shear along a surface-based convergence zone. The convergence zone intensified an d developed upward with a circulation center directly beneath the updraft e ventually contracting to the scale of a tornado vortex. After tornadogenesi s, the previously disorganized thunderstorm displayed characteristics commo nly associated with supercells, such as a hook echo, bounded weak-echo regi on, a WSR-88D algorithm detection of a mesocyclone, and a visible wall clou d. The mountaintop WSR-88D was able to identify the tornado in the base veloci ty data and via the latest operational version of the Tornado Detection Alg orithm. However, interpretation of velocity products produced by the radar system for real-time operations was problematic due to degradation with ran ge of the displayed data. Without access to the full-resolution velocity da ta in real time, it would be impossible for a forecaster to corroborate the algorithm tornado detection.