![]() NWS Weather Forecast Offices (WFOs) are responsible for issuing severe thunderstorm and tornado warnings as storm-based polygons that are intended to represent the area that a convective weather hazard is expected to affect for the duration of the warning, typically on the scales of 0–60 min and 10–100 km 2 ( NWS 2020a). This is particularly noteworthy for storms expected to live longer than the average warning duration (30 or 45 min) such as long-tracked supercells that are more prevalent during significant tornado outbreaks. This all results in greater average lead times and lower average departure times than current NWS warnings, with little to no impact to average false alarm time. In addition, warnings are automatically cleared from locations where the threat has passed. ![]() TIM mitigates gaps in warning coverage and improves the handling of storm motion changes. When forecaster workload is high, storms remain continually tracked and warned. This provides more uniform, or equitable, lead time for all locations downstream of the event. With TIM, a warning polygon is attached to the threat and moves forward along with it. This concept is proposed as a first stage for implementation of the Forecasting a Continuum of Environmental Threats (FACETs) paradigm, which eventually aims to deliver rapidly updating probabilistic hazard information alongside NWS warnings, watches, and other products. Threats-in-Motion (TIM) is a warning generation approach that would enable the NWS to advance severe thunderstorm and tornado warnings from the current static polygon system to continuously updating polygons that move forward with a storm.
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