Tornado analysis using a "tornado-day" approach was made for the State of Missouri, and its climatic divisions, for the period 1950-2002. Although tornado days have not increased in Missouri, the NW Prairie climatic division recorded a statistically significant decline in tornado days during that time period. Seasonal patterns in tornado days were examined for each of the 115 counties in Missouri using cluster analysis. It revealed that the duration of the "tornado season" varies somewhat across Missouri, several southern counties being affected by a bimodal seasonal pattern in tornado days. The interannual tornado-day time series was examined for Missouri, spectral density estimates showing periodicities of 2.1, 2.8, 8.5, 11.6, and 12.8 yrs. Cross-amplitude analysis revealed that these tornado-day periodicities appear to be connected to fluctuations affecting the Pacific-North American patterns (PNA)—(8.5 yrs.), and quasi periodicities associated with the Southern Oscillation and the El Niño 3.4 indexes (11.6 to 12.8 yrs.).