Evaluating Impact-Based Warning Guidelines for Tornado Emergency Issuance

Le résumé fourni par la source

Tornado emergencies (TOREs) were first used in 1999 by the National Weather Service (NWS) to effectively warn of tornadoes capable of catastrophic damage. After years of informal use, a formal version of the TORE was developed and gradually introduced to weather forecasting offices through the impact-based warning (IBW) program. Along with IBWs, the Warning Decision Training Division (WDTD) introduced a set of guidelines that NWS forecasters can use to issue TOREs. The guidelines recommend that a forecaster upgrade a tornado warning to a TORE if the significant tornado parameter (STP) is ≥ 6 in the storm's environment, the rotational velocity (VROT) is ≥ 70 kt on radar, and there is radar or spotter confirmation of a tornado. Since the introduction of TOREs, minimal work has explored how closely NWS forecasters follow the WDTD IBW guidelines when issuing TOREs. For the 89 IBW TORE cases from 2014-2023, VROT was obtained from GR2Analyst, and fixed- and effective-layer STP was calculated using Metpy from the NOAA Rapid Refresh (RAP) model. Our analysis indicates that NWS forecasters often did not adhere to the recommended guidelines, as only two TORE cases met both STP and VROT thresholds. However, 70% of TORE cases covered tornadoes that were rated EF-3+, and 91% of all TORE cases had a TDS present. Population density was also once a guideline for TORE issuance, but has subsequently been omitted. Currently, NWS forecasters are being interviewed to determine the best practices of TORE issuance to potentially inform an updated set of guidelines.

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