TIM is more temporally-specific, and provides meaningful information about times of arrival and departure. In addition, TIM can also support the capability to provide automated “all clear” information when the threat has passed. When forecaster workload is high, storms remain continually tracked and warned. This provides equitable lead time for all locations downstream of the event (Fig. With TIM, a warning polygon is attached to the threat and moves forward along with it (Fig. Actual NWS tornado warning polygons (yellow) for the storm that impacted Lee County, AL, on 3 March 2019. Two users, A and B, received inequitable lead time. Present day warning paradigm: Idealized event with a moving storm threat (circle) and two separate Severe Thunderstorm Warnings issued 55 minutes apart. In some cases, the workload of the forecaster is too great to keep up with the issuance of new downstream warnings, and sometimes a storm can move out of a current polygon and become unwarned. This is particularly noticeable for long-track tornado events (Fig. With each subsequent warning in the series, this behavior continues. Nearly adjacent locations can have dramatically different lead times if one location is just outside the upstream warning. This frequently results in non-uniform lead times for those who are on the border of a severe thunderstorm or tornado warning. What are the disadvantages of the current warning system?Ĭurrently, when NWS forecasters issue warnings for long-lasting severe thunderstorms, the storms are handled by a series of separate warning polygons that are issued one after the other, often with little overlap, as a storm moves along a path (Fig. TIM is essentially PHI, but without the probabilities (which will come later as the science evolves).īecause weather is continuously updating! Data used for severe weather forecast and warning decision making is updating continuously, ranging from radar, satellite, lightning, near-storm environment, as well as guidance algorithm data such as Multiple-Radar/Multiple-Sensor (MRMS) and ProbSevere – each which update at 1- to 2-minute intervals. TIM polygons update every minute, and march forward with the storm threat. TIM are NWS Severe Thunderstorm Warnings and Tornado Warnings represented by continuously-updating warning polygons. Top: a continuously-updating Probabilistic Hazard Information (PHI) plume Bottom: AWIPS2 Hazard-Services-Probabilistic Hazard Information (HS-PHI) showing multiple hazard plumes. PHI can be used to provide custom user-specific products that can be tailored to adapt to a variety of needs – for example, providing longer lead times, at lower confidence, for more vulnerable populations with a lower tolerance for risk.įigure 1. Probabilistic Hazard Information (PHI) are continuously-updating probabilistic hazard grids (Fig. FACETs-Severe is focused on severe convective weather, such as tornadoes, thunderstorm winds, hail, and lightning. A simple change in the way warnings are generated can achieve major improvements.įorecasting A Continuum of Environmental Threats (FACETs) is a next-generation forecast and warning framework that is modern, flexible, and designed to communicate clear and simple hazardous weather information to serve the public, extending from days to within minutes of an event for all environmental threats. This concept is proposed as a first stage for implementation of the Forecasting a Continuum of Environmental Threats (FACETs) paradigm for severe weather warnings. 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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