Assessing Storm Prediction Center Tornado Outbreak Forecasts using Synoptic-Scale Composite Analysis

Tornado outbreaks can lead to loss of life and property. Therefore, it is imperative that forecasts of these phenomena are as accurate as possible. The Storm Prediction Center (SPC) is tasked with forecasting tornado outbreaks on the national scale, and since tornado-producing storms are strongly driven by synoptic-scale influences, it is important to identify the synoptic-scale influences that may contribute to inaccurate outbreak forecasts. This project seeks to find these synoptic-scale influences by assessing composite fields of tornado outbreaks the SPC correctly and incorrectly forecasted. Events from 2006-2012 were considered. Using SPC's archived convective outlook tornado probabilities and outbreak days with seven or more tornado reports, a distribution of the percentage of reports within the forecast 10% probability contour will be formulated. Quartiles of events from this distribution will be extracted. Base-state synoptic-scale meteorological variables from the NCEP/NCAR reanalysis dataset from each quartile will be used in the formulation of the composites. Additionally, another composite will be created of the “false alarms,” the days during which a 10% probability was forecasted but less than seven tornadoes were reported. These composites will be statistically analyzed for synoptic scale differences. It is expected there will be meaningful differences that might be of use to forecasters in the future.