The Tornado Climatology of the St. Louis Weather Forecast Office
 County Warning Area

Mark F. Britt and Fred H. Glass

NOAA/National Weather Service Forecast Office
12 Research Park Drive
St. Charles, Missouri 63304

Clearly the most important task facing the National Weather Service (NWS) field office forecaster is
the prediction and warning of severe local storms.  At the very foundation of the forecast and
warning decision process is a knowledge of the climatology of the severe weather events.  In this
study we investigate the occurrence of strong and violent tornadoes (F2-F5) for the County Warning
Area (CWA) of the NWS Forecast Office St. Louis (NWS LSX).  The NWS LSX CWA
encompasses 46 counties in central and eastern Missouri and portions of western Illinois, with an
approximate population of 3.3 million.  Tornado reports from the NWS Prediction Center data base
and the NOAA Publication Storm Data were examined for the years 1950 - 1999.  The yearly,
monthly and hourly distribution of strong and violent tornadoes (F2-F5) is presented.  Reports are
also grouped together to determine the occurrence and frequency of significant outbreaks.

Preliminary results indicate some interesting aspects regarding the occurrence of violent tornadoes
(F4-F5) during the study period.  While the greatest number of all tornadoes (F0 and higher) occurs
from April through early June, the number of violent tornadoes is split equally between spring and
winter months.  For the immediate St. Louis metropolitan area, the climatology shows a decided
preference for violent tornadoes during the late evening-early morning hours of the winter.

The desired goal in developing this climatology is to give forecasters greater insight into the
commonalities and probabilities of an event occurring, and prompt a higher state of awareness
even before the first thunderstorm forms.  This is the first step toward developing a synoptic
climatology of severe weather events across central and eastern Missouri and portions of western 

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