Climatology of Null Severe Outbreak Events

Tornado outbreaks impact millions of lives; thus, it is imperative meteorologists know the precursors of these events to their fullest capabilities. Currently, Storm Prediction Center (SPC) forecasters utilize synoptic-scale and mesoscale precursors in their long-term forecasts. Since synoptic conditions have higher predictability in numerical simulations, it is essential to improve understanding of the role of synoptic-scale processes in tornado outbreak occurrence. To gain perspective on synoptic conditions' role in tornado outbreaks, composites of several outbreak events will be analyzed. The synoptic conditions of four events between 2001 and 2010 for which SPC correctly forecasted tornado outbreaks will be compared with those of two “false alarm” events during which an outbreak was forecasted but did not materialize and two events during which a tornado outbreak occurred but was not predicted. For the two former cases, days with tornado probabilities, as defined by the SPC, of 10% or greater will be considered. The criteria for the latter class include lower than 10% tornado probabilities combined with seven or more reported tornadoes. Using NCEP/NCAR Reanalysis data, composite averages of three-dimensional fields of common synoptic-scale variables will be computed. These composites will then be scrutinized for similarities and differences. It is expected there will be discernible differences between these cases and conclusions will be drawn about the role synoptic conditions play in tornado outbreak forecasting.