Identifying Environmental Precursors of Tornadic Supercells Within NSSL's Warn-on Forecast System

Recent research on NSSL’s Warn-on Forecast System (WoFS) has focused on probabilistic products and storm-centric parameter fields, but formal exploration of environmental fields has yet to be performed. Pockets of enhanced values for environmental parameters have been observed in the inflow regions of supercells within the ensemble, but these need to be better characterized and understood to increase their effective use in short-term forecasting. After using Storm Data and an automated supercell identification method to identify 70 EF1+ tornadic supercells during 2017-2021, a suite of environmental convective parameters from the WoFS ensemble are examined at the storm-scale in the hour leading up to the tornado. Additionally, we compare results for the 70 tornadic storms to severe but non-tornadic supercells that produced large hail and high wind. Our goal is to determine whether WoFS provides reliable and consistent environmental precursors for tornadoes at lead times up to an hour. Probability-matched composite means of environmental fields that are centered on the intensifying supercells reveal distinct features that are present in WoFS just prior to tornado occurrence. These include expected features such as a local maximum in CAPE, minimum in LCL, and maximum in the 0-1 km storm relative helicity in the storm inflow region. Differences are clearly seen in the distribution of these factors between tornadic and nontornadic supercells. This work can help forecasters develop trust in WoFS, enabling its effective use during the leadup to tornadoes.