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Examining Subdaily Tornado Warning Performance and Associated Environmental Characteristics

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  • 1 a Center for Risk and Crisis Management, University of Oklahoma, Norman, Oklahoma
  • | 2 b Cooperative Institute for Mesoscale Meteorological Studies, Norman, Oklahoma
  • | 3 c NOAA/NWS/Storm Prediction Center, Norman, Oklahoma
  • | 4 d NOAA/OAR/National Severe Storms Laboratory, Norman, Oklahoma
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Abstract

Increasing tornado warning skill in terms of the probability of detection and false-alarm ratio remains an important operational goal. Although many studies have examined tornado warning performance in a broad sense, less focus has been placed on warning performance within subdaily convective events. In this study, we use the NWS tornado verification database to examine tornado warning performance by order-of-tornado within each convective day. We combine this database with tornado reports to relate warning performance to environmental characteristics. On convective days with multiple tornadoes, the first tornado is warned significantly less often than the middle and last tornadoes. More favorable kinematic environmental characteristics, like increasing 0–1-km shear and storm-relative helicity, are associated with better warning performance related to the first tornado of the convective day. Thermodynamic and composite parameters are less correlated with warning performance. During tornadic events, over one-half of false alarms occur after the last tornado of the day decays, and false alarms are 2 times as likely to be issued during this time as before the first tornado forms. These results indicate that forecasters may be better “primed” (or more prepared) to issue warnings on middle and last tornadoes of the day and must overcome a higher threshold to warn on the first tornado of the day. To overcome this challenge, using kinematic environmental characteristics and intermediate products on the watch-to-warning scale may help.

Significance Statement

This study examines the performance of tornado warnings during past severe weather events in an effort to better understand forecasting strengths and weaknesses. On days with multiple tornadoes, we find that the first tornado of the day is less likely to be warned and that, if it is warned, it has less lead time than the other tornadoes on the same day. Furthermore, there are some environmental factors (such as bulk wind shear) that influence the likelihood that the first tornado is warned. This study helps forecasters to understand which environmental traits may be more useful for better anticipating the first tornado of the day.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Makenzie J. Krocak, makenzie.krocak@noaa.gov

Abstract

Increasing tornado warning skill in terms of the probability of detection and false-alarm ratio remains an important operational goal. Although many studies have examined tornado warning performance in a broad sense, less focus has been placed on warning performance within subdaily convective events. In this study, we use the NWS tornado verification database to examine tornado warning performance by order-of-tornado within each convective day. We combine this database with tornado reports to relate warning performance to environmental characteristics. On convective days with multiple tornadoes, the first tornado is warned significantly less often than the middle and last tornadoes. More favorable kinematic environmental characteristics, like increasing 0–1-km shear and storm-relative helicity, are associated with better warning performance related to the first tornado of the convective day. Thermodynamic and composite parameters are less correlated with warning performance. During tornadic events, over one-half of false alarms occur after the last tornado of the day decays, and false alarms are 2 times as likely to be issued during this time as before the first tornado forms. These results indicate that forecasters may be better “primed” (or more prepared) to issue warnings on middle and last tornadoes of the day and must overcome a higher threshold to warn on the first tornado of the day. To overcome this challenge, using kinematic environmental characteristics and intermediate products on the watch-to-warning scale may help.

Significance Statement

This study examines the performance of tornado warnings during past severe weather events in an effort to better understand forecasting strengths and weaknesses. On days with multiple tornadoes, we find that the first tornado of the day is less likely to be warned and that, if it is warned, it has less lead time than the other tornadoes on the same day. Furthermore, there are some environmental factors (such as bulk wind shear) that influence the likelihood that the first tornado is warned. This study helps forecasters to understand which environmental traits may be more useful for better anticipating the first tornado of the day.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Makenzie J. Krocak, makenzie.krocak@noaa.gov
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