Convective season synoptic climatology by ENSO phase in the north central United States

The El Niño/Southern Oscillation (ENSO) is known to affect synoptic patterns across the continental United States, particularly by its impact on the upper tropospheric jet stream position, which in turn affects mid-tropospheric ridge and trough locations and thus areas favorable for temperature and precipitation anomalies. These global circulation patterns influence synoptic weather patterns, which in turn influence regional severe weather activity. Though it is one of several factors associated with the potential for severe weather, the synoptic environment plays a key role in severe weather potential by providing favorable ingredients for the development of severe convection. While ENSO is one of many factors that influence global circulations, and by distillation may have a less distinguishable influence on the synoptic pattern, this study will investigate whether coherent signals can be uncovered in the synoptic environment, based on ENSO phase, that would influence the potential for severe convection in the north central United States.

Utilizing the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data available via NOAA's Climate Diagnostics Center, the convective peak season of March through June will be examined, based on ENSO phase as determined by NOAA's Climate Prediction Center, for the period 1950 to 2005. Previous research has indicated potential statistical relationships between the climatology of tornadoes and ENSO phase in the north central United States, specifically in a nine-state area extending from North Dakota to Illinois. This study will investigate potential physical causes of the statistical changes to severe weather climatology, determining whether changes in the climatology of severe convection can be attributed to changes in the synoptic environment during the three ENSO phases.