This is Severe Weather Awareness Week (SWAW) in Iowa and the topic for Monday is Severe Thunderstorms. The NWS classifies such storms as those producing at least 58 MPH wind gusts and/or one inch diameter hail. When the conditions are favorable for organized and fairly wide- spread severe thunderstorm development, the NWS coordinates the issuance of a Severe Thunderstorm Watch between the Storm Prediction Center in Norman, OK and the local forecast offices within the threat area. Such watches are hopefully issued with meaningful lead time before any storms require the issuance of a warning. The featured chart presents some metrics on the time duration of Severe Thunderstorm Watches for Story County, IA. The orange line presents the accumulated frequency of the watch duration at issuance. The blue line represents the final duration after watches are cancelled early. Most watches extend out between six and eight hours and end up lasting about two to seven hours. The difference between the two is often explained by the storm threat passing to the east of the county as the storm complex passes through.

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