Finding the Best Link Between SPC Tornado Forecast Verifications and Known Severe Weather Parameters

Ever since the Storm Prediction Center (SPC) started issuing nationwide severe weather outlooks that include probabilistic forecasts for tornadoes, many lives and property have been saved. The goal of the study was to understand whether there are differences in commonly used severe weather forecast parameters that differentiate successful SPC forecasts from SPC forecast busts. We examined, streamwise vorticity (ω_s), storm relative helicity (SRH), convective available potential energy (CAPE) and entraining CAPE (ECAPE). A case day for this study was defined with outlooks and tornadoes occurring between 12z-12z the next day. All days that had a tornado risk >15%, (E)F4-5, and a few special cases were compiled into a list of 133 case days from 2003-2022. Environmental data was collected from the ERA5 reanalysis model to create soundings to be analyzed for each day. It was found that ω_s and SRH, both being measurements of shear, in the lowest kilometer had the greatest chance of differentiating if a day was going to produce many tornadoes. Meanwhile the different types of CAPE had no correlation between low producing day and the big outbreaks. Other indicators appeared to be lower LCL, CIN, higher storm speeds, more curved and wider hodographs, and slightly lower surface temperatures. The true skill statistic (TSS), which tells how good a variable is a differentiating high and low events ranging from 0 being the worst to 1 being perfect. The TSS values of ω_s was 0.52, SB CAPE was 0.02, and SPC forecasts were 0.41. Shear appears to be better than CAPE at being able to determine how a SPC tornado outlook will pan out.