Historical Tornado Cases for Saint Louis County Warning Area
of Eastern Missouri and SW Illinois
19 cold season cases(October to March) and 15 warm season cases were analyzed. In 16 of the 19 cold season cases the
surface based CAPE was near or greater than 1000j/kg. In 2 of these 19 cases the CAPE was around 1000j/jg. In 4 cases
the CAPE was greater then 1600j/kg. The CAPE was highest in the December 2, 1982 case with 2200j/kg. The lowest CAPES
|were on January 3, 1950(850j/kg), February 10, 1959 (800j/kg) and November 15, 1988(800j/kg). The average surface based
CAPE was 1200 j/kg in the cold season.The CAPE was 3000j/kg or greater in all 5 May and June cases. The CAPE was
between 1500j/kg and 2400j/kg in 6 of 7 April cases.
The warm frontal cases and warm sector cases(out ahead of cold front) were about equally divided when cold and warm
season cases are included. But warm sector cases were much more prevalent in the cold season while a majority of cases
in the warm season were east or se of the sfc low along the warm front or stationary front. Of the 21 cold season cases (1938
cases added), warm frontal tornadoes only occurred in 6 cases, whereas there were warm sector tornadoes in 17 of the 21
cases. Of these 17, 11 occurred out ahead of a cold front, 4 occurred along outflow boundaries ahead of a cold front in the
warm sector and 2 occurred along pre-cold frontal troughs.
Most of the cases were associated with intense and progressive shortwave troughs with deep surface lows. In only 5 cases
out of 34 was the sea level pressure with the center of the surface cyclone or trough greater than or equal to 1000mb. In 20
of 34 cases the sea level pressure was less than 995 mb. In 9 cases of 34 the surface pressure was less than 990mb. In 29 of
34 cases the sea level pressure was below 1000mb in the center of the surface cyclone or trough.
The surface dewpoint was less than 60F in only 4 cases of 33. There were no cases with less than a 57F surface dewpoint. All
the cases with less than a 60F dewpoint were in December, January or February.