Tornado Formation and Intensity Prediction Using Polarimetric Radar Estimates of Updraft Area

A sample of 198 supercells are investigated to determine if a radar proxy for the area of the storm midlevel updraft may be a skillful predictor of imminent tornado formation and/or peak tornado intensity. A novel algorithm, a modified version of the Thunderstorm Risk Estimation from Nowcasting Development via Size Sorting (TRENDSS) algorithm is used to estimate the area of the enhanced differential radar reflectivity factor (Z_DR) column in Weather Surveillance Radar–1988 Doppler data; the Z_DR column area is used as a proxy for the area of the midlevel updraft. The areas of Z_DR columns are compared for 154 tornadic supercells and 44 nontornadic supercells, including 30+ supercells with tornadoes rated EF1, EF2, and EF3; 8 supercells with EF4+ tornadoes also are analyzed. It is found that (i) at the time of their peak 0–1-km azimuthal shear, nontornadic supercells have consistently small (<20 km²) Z_DR column areas, while tornadic cases exhibit much greater variability in areas; and (ii) at the time of tornadogenesis, EF3+ tornadic cases have larger Z_DR column areas than tornadic cases rated EF1/2. In addition, all eight violent tornadoes sampled have Z_DR column areas > 30 km² at the time of tornadogenesis. However, only weak positive correlation is found between Z_DR column area and both radar-estimated peak tornado intensity and maximum tornado path width. Planned future work that focuses on mechanisms linking updraft size and tornado formation and intensity is summarized and the use of the modified TRENDSS algorithm, which is immune to Z_DR bias and thus ideal for real-time operational use, is emphasized.