Tornado Warnings are issued to enable the public to get out of harm’s way and mitigate preventable loss. NWS forecasters issue approximately 2,900 Tornado Warnings per year, primarily between the Rockies and Appalachian Mountains. Tornado Warning statistics are based on a comparison of warnings issued and weather spotter observations of tornadoes and/or storm damage surveys from Weather Forecast Offices in the United States. Lead Time (LT) for a Tornado Warning is the difference between the time the warning was issued and the time the tornado occurred (based on certified reports) in minutes, assuming the tornado tracked within the bounds of the warned area. Lead Times for all tornado occurrences within the U.S. are averaged to get this statistic for a given fiscal year. This average includes all warned events with zero lead times and all unwarned events. Lead Time is calculated down to the minute for individual Tornado Warnings and tornadic events. Although the timing of the warning transmission is recorded to the nearest second, typically there is only an estimate to the nearest minute of when a tornado touches down. Additionally, even though we can compute the average tornado warning lead time to a precision of 30 second increments or less, the reporting of this value implies greater accuracy in the data based on scientific and logistical restrictions on tornado reporting and surveying. Most tornadoes cannot be visually tracked from beginning to end and post-storm damage surveying is the official method with which the NWS categorizes tornado characteristics (intensity, path length & width) but must rely on radar data to estimate the timing of the tornado track.

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