As a part of the National Weather Service's mission of protecting life and property, they issue watches and warnings for storms capable of producing damaging winds, hail, and/or tornadoes. The watch is typically issued ahead of time when conditions are favorable for severe storms to develop and a warning is issued when severe conditions are imminent. Of course, not all NWS warnings occur within an area that is currently under a watch. The featured chart looks into this frequency by computing the percentage of severe thunderstorm or tornado warnings that were issued when a watch was in effect for the warned county. The data is partitioned by month as there is a clear annual signal to this metric and is easily explained. Watches are issued for organized severe weather events that have considerable spatial and temporal scale. Summer time severe weather is very often isolated, slower moving, and limited to the late afternoon during peak heating, all of which don't lend well to the watch process.

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Tags:   watch   warning