Climatological factors, including the phase of the El Niņo-Southern Oscillation (ENSO), are known predictors for seasonal forecasts of temperature and precipitation. ENSO and other climatological factors also have a relationship to the severe weather potential in a given convective season, identifying predictors to elements such as number tornado days and number of significant tornadoes. While seasonal predictions of severe weather potential are not much aid for daily operations, they can be used by emergency managers, the media, and forecasters to increase preparedness for seasons that have the potential for above normal convective activity.

Utilizing a standard compositing methodology developed within the National Weather Service, as well as the NOAA standard definition of ENSO to determine phases for each season, this study develops a climatology of tornado and severe thunderstorm activity in the central Plains and northern Mississippi River valley areas based on ENSO phase and analyzes the potential for a predictable shift in the climatology during the three ENSO phases. The study will also address regional differences in ENSO signal and climatology in a nine-state area from North Dakota to Illinois, identifying how the impact of ENSO changes from state to state within the study area.