This study is a preliminary examination of the synoptic conditions associated with significant tornadoes (F2-F5) in the NWS St. Louis County Warning Area (CWA). A climatology of 36 tornadoes that occurred on 18 days from November through February during the 50 year period covering 1950-1999 is presented. A previous analysis of the complete climatology indicated that significant tornadoes comprise a larger percentage of all tornadoes that occur during the late autumn and winter. A closer examination of the cool season subset shows the transition from autumn to winter (November and December) is the most active time for cool season tornadoes with no favored time of day.

Composites of upper air analyses are examined in an effort to find common synoptic patterns associated with such tornadoes. Preliminary results suggest all cases occur in strongly dynamic patterns with nearby upper-level jet streaks associated with progressive shortwave troughs. Each case also possessed a sharply baroclinic, low-level boundary moving into anomalously high moisture rich air, transported northward on a strong low-level jet. Data from regional soundings are stratified to determine how background atmospheric conditions compare to accepted kinematic and thermodynamic parameters. In addition, soundings that occur in close temporal and spatial proximity to individual tornadoes are presented. Our study determined these soundings tend to possess weak thermodynamic profiles (CAPE < 1000 J/kg), however the wind fields associated with these systems lead to significant kinematic parameters (0-6km shear >20 m/s, SREH > 450 m2/s2).