Vol 10-1 2015

The Joplin, Missouri EF5 tornado event on 22 May 2011 prompted the Central Region of the National Weather Service (NWS) to re-evaluate the current tornado warning format and implement the impact-based tornado warning (IBTW) experiment.  IBTWs consist of tiers including damage tags and impact wording that convey increasing levels of damage.  The damage wording within an IBTW is shown to relate to the Enhanced Fujita (EF) scale.  Wording included in non-tagged IBTWs corresponds to EF0-EF2 tornado damage, while the damage wording for tagged IBTWs corresponds to EF3-EF5 tornado damage.  This study investigates the accuracy of IBTWs by examining if a tornado occurs during the warning time frame, and whether the resulting damage matches the damage wording in the IBTW.  All IBTWs from 1 April 2013 through 30 November 2013 were collected, as well as tornado survey information.  Using these survey data, IBTWs were verified by the intensity of the tornado, if one occurred.  Probability of detection (POD) and false alarm ratio (FAR) statistics are calculated through 2×2 contingency tables for both non-tagged and tagged IBTWs.  Results indicate that the majority of both non-tagged and tagged IBTWs are false alarms, and tagged IBTWs have a very low POD.  Other studies have shown that limitations in current technology and scientific knowledge may contribute to false alarms and missed detections.  Case studies are examined to analyze whether these limitations play role in the use of IBTWs.