NOAA's National Weather Service Weather Forecast Office

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 Illinois.