A terrible tragedy occurred on Friday evening, as strong tornadoes struck across a multi-state swath from Arkansas through Kentucky. Early estimates suggest that 50-100 individuals lost their lives and hundreds were injured.
A destroyed candle factory in hard-hit Mayfield, Kentucky
The death toll was undoubtedly enhanced by the nighttime occurrence of these storms and their development during the winter season, which is unusual but not unprecedented. The storms occurred in two coherent lines oriented southwest to northeast, as shown by the tornado reports (red dots) provided by the NOAA/NWS storm prediction center. For reference, the tornadoes hit Mayfield, KY around 10 PM Friday evening.
My colleagues at the National Weather Service (NWS), both at the Storm Prediction Center and the local NWS forecast offices (such as Paducah, Kentucky) did an excellent job in predicting the threat and provided timely watches and warnings before the tornadoes struck.
Surely these skillful forecasts and timely warnings saved lives. But they weren't enough to prevent massive loss of life.
In this blog, I will review the forecasts/warnings and suggest that new smartphone-based warning systems are both needed and possible. Technology that could save many lives from such severe storms.
The National Weather Service Forecasts
Earlier that day (1:17 PM), the Paducah National Weather Service Office noted that the expected meteorological conditions were similar to those accompanying previous cool-season tornado outbreaks (see below).
Furthermore, at the same time, the NOAA/NWS Storm Prediction Center (SPC) put out a tornado watch that encompassed Mayfield and other locations that were later hit by tornadoes (see below).
Later in the afternoon, the watches were repeated and became more strident, and as severe thunderstorms, with supercell structure and rotation developed, tornado warnings (which indicate an imminent threat) were communicated (see below for 3:29 PM CST).
The tornado warning made by the NWS Office at Paducah for Mayfield at 9:03 PM was stunningly good (see below). This warning was communicated roughly30 minutes before Mayfield was devastated.
I could show you more NWS forecasts, model predictions, and more...and you would be impressed. The region was given skillful and timely warnings about the potential for strong, damaging tornadoes. NWS forecasters and the NOAA/NWS Storm Prediction Center staff can be proud of what they did.
But many people still died.
I would suggest that the technology exists to mitigate the tornado risk substantially. A technology I have been thinking about for quite a while: automated smartphone-based warning systems, driven by state of science observations. But first, let's talk about the nature and limitations of severe storm and tornado forecasting.
Limitations of Tornado Forecasting
Forecasting technology for severe thunderstorms has come a long way during the past decades. Meteorologists have high-resolution forecasting models (such as NOAA/NWS High-Resolution Rapid Refresh HRRR), improved meteorological radars and satellite systems, improved knowledge of the structure and evolution of severe convective storms and machine-learning techniques now assist severe storm prediction (see model forecast below).
9-h NOAA/NWS HRRR model Forecast at 03 UTC 11 December (9 PM CST 10 Dec)
Improved models and forecast guidance help meteorologists recognize threatening situations and predict the occurrence of severe storms for a region. However, roughly three hours or more out, our models cannot predict the exact locations and intensities of incipient severe storms. Only when the storms have developed and are moving on clear paths can forecasters provide detailed forecasts of tornado occurrence and track....and even then, only for the next few hours.
I should note that NWS tornado warnings have a False Alarm Rate (FAR) of roughly 70%. So approximately 70% of the warnings don't pan out.
From experience, people and businesses know that the forecasts are not perfect and thus don't necessarily act promptly or effectively to shelter in place or move away from the threat. And then there is the issue of communication....they may not even know of the threat.... particularly an issue for nighttime storms.
The Predictability of the Recent Event
An important point about the recent event was that the tornadoes were long-lived and moved on a relatively straight, continuous path. Large, intense tornadoes are often associated with supercell thunderstorms with rotation updrafts. We can see the large areas or rotation using Doppler radars, which tell us the velocity towards or away from the radar of the precipitation associated with the storm
As shown in the figure below, alternating colors (in this case red and green) in a small region are the sign of rotation in the radar-based Storm Relative Motion (SRM) imagery:
Here is an animation of the SRM imagery from the Paducah radar during the period before the tornado hit Mayfield. The rotation start was moving straight to the NW with little change in intensity.
We can track this rotation over time, and doing so, the path of rotating storms for the period around the worse tornado occurrence on Friday evening is shown below. You can see the amazingly straight path of the narrow zone of rotation that extends from Arkansas, into Tennessee, and Kentucky. There is also a line of rotation associated with other severe storms to the north.
The point of all this is that simple extrapolation of severe storm motion provided an excellent short-term forecast for the next hour or so for this event.
Tornado guidance must be delivered in real-time to individuals or businesses, so they can make optimal, immediate decisions to save life and property. For tornadoes, folks must determine whether they are threatened at all, and, if so, whether to shelter in place or to get out the way of the storm.
Smartphone-Based Tornado Warning App
Almost everyone has a smartphone and such phones know exactly where they are since they have GPS.
Now obviously, we could feed National Weather Service forecasts, including tornado watches and warnings, to smartphones, providing the forecasts appropriate to the location in question. This is low-hanging fruit...and obvious.
But in active situations, things are happening too fast and too localized for NWS forecasters to be guiding people....automated software has to take over.
Using Doppler radar imagery (which is available roughly every 5 minutes), the instantaneous path of the storm could be determined in real-time and the storm's location and path could be made available on the smartphone, with constantly updated information on the probability that the smartphone's location being overrun. The estimated time of arrival could be noted. But there is more. Modern radars can also track the debris cloud of major tornadoes....and thus have confirmatory information of the position and movement of the tornado vortex
The smartphone could not only provide a warning of imminent tornado passage but could provide information on the best direction to flee if no sheltering location is available--generally at right angles to the storm path. A distance of a few thousand feet can make a huge difference if there is no place to shelter.
It is also possible that smartphones THEMSELVES can provide critical weather information to facilitate determining tornado location and movement. Many smartphones possess very capable pressure sensors, something I know about because I have been researching the meteorological applications of such sensors for over a decade.
Tornadoes have a large pressure signature and smartphones could collect and communicate such pressures in real-time. Such smartphone pressures observations could be used by automated systems to determine tornado intensity and path, and thus improve guidance to individuals making critical decisions.
I have tried talking to Apple and Google about helping collect smartphone pressure data to improve weather forecasts. So far, they have listened politely and done nothing. Perhaps that could change. Or perhaps Amazon could help.
In summary, a smartphone app, applying real-time meteorological data, could provide extraordinary valuable guidance during tornado outbreaks, and perhaps save many lives.
It could be done. And I suspect only a government organization would take it on because of liability concerns.
Post a Comment