Some-Me Variability: A Climatology of Missouri Tornadoes

Due to the culmination of several factors including geographical location and a wide range of terrain types, the state of Missouri presents many challenges to the modern-day forecaster. Despite such difficulties, recent studies have shown that Missouri's weather patterns exibit impressive interannual variability that can be related to the El Nino and Southern Oscillation (ENSO). Thorough knowledge of such variability can be useful for both long-term and short-term forecasting and planning. This study will focus on trends in the occurrence and the interannual variability of significant tornadoes throughout the state of Missouri. For this study, the climatology of significant tornadoes and significant tornado days were compiled for the state of Missouri from 1950 - 1999 was created in order to examine the issues stated above. Initial results show that there was a weak downward trend in the number of tornado days. This trend counters the upward trend in tornado activity nationally, which is due in part to better observational methodologies. Also, as was found for other characteristics of the climate of Missouri, significant ENSO related variability was found. It was found that there were significantly more tornadoes and tornado days during La Nina years, than during El Nino or Neutral years. In examining this issue further, it was determined that the more active La Nina years are a function of an increase in the number of tornado outbreaks rather than the occurrence of larger outbreaks. Finally, the issue of longer-term interannual variability is examined in order to determine if ENSO-related variability is modified by interdecadal variability such as that related to, for example, the Pacific Decadal Oscillation.