Operational Use of Experimental Warn-on-Forecast Guidance Prior to the 16 May 2017 Elk City, Oklahoma Tornado

An EF2 tornado struck Elk City, Oklahoma, on 16 May 2017, killing one person and injuring eight others. Prior to the deadly tornado, a Warn-on-Forecast prototype increased forecaster confidence for significant tornadoes in western Oklahoma. As part of WFO Norman’s seasonal readiness training, forecasters evaluated output from the National Severe Storms Laboratory’s (NSSL) Experimental Warn-on-Forecast System for ensembles (NEWS-e), a real-time Warn-on-Forecast prototype. Forecaster feedback helped NSSL scientists incorporate operationally relevant features on the NEWS-e website and familiarized forecasters with the tool for use in warning operations.

Before supercell thunderstorms initiated on 16 May, NEWS-e output depicted dangerous storms forming and moving toward western Oklahoma. This output was displayed on WFO Norman’s situational awareness display, and a University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies scientist provided a briefing on the guidance in the operations area. Once storms developed, NEWS-e contributed to a high degree of forecast confidence that the storms would become long-lived supercells with a risk of tornadoes. Based on output from NEWS-e, WFO Norman issued an advisory stating “a high probability that tornado warnings will be issued” for parts of four counties in western Oklahoma nearly two hours before the deadly tornado struck Elk City.

This use of NEWS-e demonstrates the feasibility of the proposed Forecasting a Continuum of Environmental Threats (FACETs) approach whereby forecasters can elevate tornado probabilities well downstream from legacy warning polygons, giving greater advance notice. NWS forecasters and NSSL researchers have been testing these concepts in the Hazardous Weather Testbed since 2015.