Insights into Predicting Tornado Development Using NEWS-e Vorticity Forecasts

This project seeks to determine if the low-level vorticity forecasts generated by the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e) offer clues for predicting tornadic activity. The vast amount of data produced by NEWS-e requires filtering to provide meaningful results that can be used in forecast decision-making.  Here, the authors create a “storm object” filter and apply it to forecasts provided by NEWS-e for six (6) different severe weather events. Candidate storm objects must exceed a maximum relative vorticity of 0.006 s^-1 and a mean updraft speed of 5 ms^-1. They are classified as tornadic if any part of the storm object is within 30 km of a tornado report. The vertical profiles of vorticity in each storm object reveal consistent mid-level vorticity maxima that vary little in height and strength across all storm objects. Any low-level vorticity maxima exhibited by the storm objects have much greater structural variability. Analysis of these structures show that the low-level maxima in tornadic storm objects are slightly lower and stronger than those in non-tornadic objects. At storm-scale, the profiles that contain low-level vorticity maxima in tornadic storm objects tend to be grouped together in a cohesive manner, whereas the profiles containing these maxima in non-tornadic storm objects are infrequent and randomly distributed. It is hoped that this study will provide information on how to best utilize the NEWS-e vorticity forecasts for short-term tornado prediction.