A Next-Generation Warning Concept of Threats-In-Motion (TIM): Highlighting the Benefits via New Verification Techniques

NWS severe thunderstorm and tornado warnings are issued as polygons that cover a two-dimensional area of expected threat of severe weather within a time period from 30 to 60 minutes. When a storm continues to remain severe, new warnings are issued downstream of previous warnings. These new warnings are usually issued in “stepwise” fashion until the storm is no longer deemed severe. This results in inequitable lead times for locations downstream from the threats. Locations at far ends of the initial warning are provided much more lead time than locations at near ends of the subsequent warning, even though both locations may physically be in close proximity to each other.

A proposed method for providing equitable lead times for all locations downstream of a present hazard, known as Threats-In-Motion (TIM), will be described. TIM polygons follow the hazards and can be updated at rapid intervals. TIM polygons also have the advantage of clearing out locations from warnings once the threats of passed without the need for issuing Severe Weather Statements. We will determine the effectiveness of TIM polygons using data over three states (MS, AL, GA) from the 27 April 2011 tornado outbreak event over the southeast United States. Using human-generated locations of mesocyclones and tornadoes at each radar volume scan interval, polygons will be automatically drawn at one-minute intervals on these truthed locations over the lifetime of the storm. Innovative geospatial warning verification techniques will be employed to highlight the benefits of TIM.