{"id":229,"date":"2021-03-16T15:53:20","date_gmt":"2021-03-16T20:53:20","guid":{"rendered":"https:\/\/inside.nssl.noaa.gov\/facets\/?p=229"},"modified":"2021-03-16T15:53:20","modified_gmt":"2021-03-16T20:53:20","slug":"threats-in-motion","status":"publish","type":"post","link":"https:\/\/inside.nssl.noaa.gov\/facets\/2021\/03\/threats-in-motion\/","title":{"rendered":"THREATS-IN-MOTION"},"content":{"rendered":"

THREATS-IN-MOTION (TIM)<\/strong><\/p>\n

Summary<\/strong><\/p>\n

Why Threats-In-Motion (TIM)?<\/b><\/p>\n

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.\u00a0 This concept is proposed as a first stage for implementation of the Forecasting a Continuum of Environmental Threats (FACETs) paradigm for severe weather warnings.\u00a0 A simple change in the way warnings are generated can achieve major improvements.<\/i><\/p>\n

What is FACETs?<\/b><\/p>\n

Forecasting A Continuum of Environmental Threats (FACETs)<\/a> 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.\u00a0 FACETs-Severe is focused on severe convective weather, such as tornadoes, thunderstorm winds, hail, and lightning.<\/p>\n

What is PHI?<\/b><\/p>\n

Probabilistic Hazard Information (PHI) are continuously-updating probabilistic hazard grids (Fig. 1).\u00a0 PHI can be used to provide custom user-specific products that can be tailored to adapt to a variety of needs \u2013 for example, providing longer lead times, at lower confidence, for more vulnerable populations with a lower tolerance for risk.<\/p>\n

\u200b\"\" \"\" <\/span><\/span>\"\"\u200b<\/span><\/span><\/p>\n

Figure 1.\u00a0 Top:\u00a0 a continuously-updating Probabilistic Hazard Information (PHI) plume; Bottom: AWIPS2 Hazard-Services-Probabilistic Hazard Information (HS-PHI) showing multiple hazard plumes.<\/em><\/p>\n

What are Threats-In-Motion?<\/b><\/p>\n

TIM are NWS Severe Thunderstorm Warnings and Tornado Warnings represented by continuously-updating warning polygons.\u00a0 TIM polygons update every minute, and march forward with the storm threat.\u00a0 TIM is essentially PHI, but without the probabilities (which will come later as the science evolves).<\/p>\n

Why continuous updates?<\/b><\/p>\n

Because weather is continuously updating!\u00a0 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.<\/p>\n

What are the disadvantages of the current warning system?<\/b><\/p>\n

Currently, 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. 2).\u00a0 This frequently results in non-uniform lead times for those who are on the border of a severe thunderstorm or tornado warning.\u00a0 Nearly adjacent locations can have dramatically different lead times if one location is just outside the upstream warning.\u00a0 With each subsequent warning in the series, this behavior continues.\u00a0 This is particularly noticeable for long-track tornado events (Fig. 3).\u00a0 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.\"\"\u200b\"\"<\/span><\/span>Figure 2.\u00a0 Present day warning paradigm:\u00a0 Idealized event with a moving storm threat (circle) and two separate Severe Thunderstorm Warnings issued 55 minutes apart.\u00a0 Two users, A and B, received inequitable lead time.<\/em><\/p>\n

\n

\"\"\"\"\u200b<\/span><\/span>Figure 3.\u00a0 Actual NWS tornado warning polygons (yellow) for the storm that impacted Lee County, AL, on 3 March 2019.<\/em><\/p>\n

What are the advantages of TIM?<\/b><\/p>\n

With TIM, a warning polygon is attached to the threat and moves forward along with it (Fig. 4, Fig. 5).\u00a0 This provides equitable lead time for all locations downstream of the event (Fig. 6).\u00a0 When forecaster workload is high, storms remain continually tracked and warned.\u00a0 In addition, TIM can also support the capability to provide automated \u201call clear\u201d information when the threat has passed [1<\/a>].\u00a0 TIM is more temporally-specific, and provides meaningful information about times of arrival and departure [2<\/a>].\u00a0 This all results in greater average lead times and lower average departure times than our current warnings, with little to no impact to average false alarm time (Fig. 7).\"\"\u200b\"\"<\/span><\/span>Figure 4.\u00a0 Threats-In-Motion (TIM) warning paradigm:\u00a0 Idealized event with a moving storm threat (circle) and one single Severe Thunderstorm Warning continuously moving with the threat.\u00a0 Two users, A and B, received equitable<\/u> lead time.<\/em><\/p>\n

\"\"Figure 5.\u00a0 Threats-In-Motion (TIM) warning polygons (gray) for the storm that impacted Lee County, AL, on 3 March 2019.<\/em>\u200b\u200b\u200b\u200b\u200b<\/p>\n

\"\"<\/span>Figure 6.\u00a0 Timeline of one-minute tornado segment lead times (min) for the Lee County, AL, tornado on 3 March 2019.\u00a0 The red arrows indicate locations where new NWS warnings became effective for that portion of the tornado track.\u00a0 NWS warning lead time (blue) shows discontinuities along path, with some locations receiving much less lead time than others.\u00a0 Threats-In-Motion (TIM) warning lead time (red) shows equitable, and greater lead time for the entire tornado.\u00a0 Times are UTC.<\/i><\/p>\n

\"\"Figure 7.\u00a0 Average lead time, average departure time, and average false alarm time for all one-minute tornado segments for the Lee County, AL, tornado on 3 March 2019.\u00a0 Units are minutes.<\/i><\/p>\n

Why not just increase the duration of our current warnings?<\/b><\/p>\n

Because this will greatly increase average false alarm area and false alarm time at the expense of the greater lead time.\u00a0 Also, locations within the warning will still have inequitable lead times<\/i>.<\/p>\n

TIM isn\u2019t just for severe thunderstorm and tornado warnings.<\/b><\/p>\n

The Storm Prediction Center is already developing Watches-In-Motion and outlooks in motion for severe convective threats.\u00a0 TIM is intended to span the entire time and space scales of severe weather.<\/p>\n

How will TIM work with the warning forecaster?<\/b><\/p>\n

TIM is already designed for AWIPS2 Hazard Services, which has already been tested during Fall 2019 and Winter 2020 at the\u200b\u200b\u200b\u200b\u200b NOAA Hazardous Weather Testbed<\/a>.\u00a0 Forecasters define 2D storm objects and determine their motion vectors, and the polygon swaths are derived from that information.\u00a0 2D object-based storm analysis improves location and motion estimates versus the point or line tracking in WarnGen.\u00a0 If the storm is expected to live beyond the typical warning duration, the forecaster turns on the Persist option.\u00a0 As with today\u2019s warning best practices for intermediate warning updates (known as Severe Weather Statements), the forecaster intervenes with the object every 15 minutes or so to modify the object shape, location, duration, motion information, and warning details.\u00a0 If the shape or motion of a storm changes, TIM allows for adjustments to the polygon without having to wait for warning to end, or issuing another potentially-confusing warning.\u00a0 The same storm could be depicted using the same ID throughout, along with a continuous history of the storm\u2019s evolution.\u00a0 When the forecaster feels the storm is nearing the end of its life-cycle, they will turn the Persist option off and let the warning naturally expire.<\/p>\n

What about short-lived storms?<\/b><\/p>\n

For short-lived storms, like pulse-severe storms, the best practice is to not persist the warnings.\u00a0 But even for non-persisting warnings, the trailing end of a TIM warning is always updating and automatically clearing out places where the hazard has already passed.<\/p>\n

Challenges.<\/b><\/p>\n

How would a rapidly-updating warning product work with the various warning dissemination technologies available, such as county-based systems (e.g., NOAA Weather Radio), and location-based systems (WEA mobile alerts)?\u00a0 We have some ideas, but need to work with experts in dissemination in both the public and private sector before we can determine if there is viability in moving forward with the TIM paradigm.<\/p>\n

In summary:<\/b><\/p>\n