Synoptic Composites of Severe Weather and Tornado Outbreaks

Mercer, A., Shafer, C. M., Doswell, C. A., Richman, M. B., & Leslie, L. M. (2010). Synoptic Composites of Severe Weather and Tornado Outbreaks. 25th Conference on Severe Local Storms. Denver, CO.

Outbreaks of severe weather affect millions of individuals nation-wide each year, occasionally resulting in catastrophic damage and fatalities. As such, a detailed understanding of the synoptic environments that drive these outbreaks is essential to help improve prediction of these dangerous events. The scope of this project is to obtain synoptic composites of tornadic and non-tornadic severe weather outbreaks in order to determine the unique synoptic characteristics of each. The synoptic composites will be formulated directly from the NCEP/NCAR reanalysis dataset, which reside on a 2.5° latitude-longitude grid. A T-mode principal component analysis of 50 tornadic and 50 non-tornadic outbreaks was conducted on five fundamental meteorological variables: temperature, relative humidity, u and v wind speed, and geopotential height, at all 17 vertical levels available in the reanalysis. The resulting 3-dimensional composites were used to initialize the WRF model in order to determine if the simulations would produce the expected outbreak of severe weather. Previous classification work was used to determine the outbreak type that the WRF was producing. Overall, results were excellent, as clear synoptic differences in each outbreak type were noted. The tornado outbreak composites were characterized by a deeper height trough, stronger thermal advection, and stronger synoptic forcings. The tornado outbreak composites also showed a deeper surface low pressure system than the non-tornadic composites. Additionally, the WRF simulations were generally correct for each composite.