Natural Hazards News

Storm Model Foresaw Tornado Precursor Hours Before Twister Hit

The experimental Warn-on-Forecast project calculates probabilities of severe weather within at-risk areas smaller than those targeted by current forecasting models.

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A rain-wrapped tornado struck the small town of Elk City, Okla., on 16 May and damaged more than 20 homes and businesses. Thanks to an experimental storm prediction model from the National Severe Storms Laboratory (NSSL) in Norman, Okla., residents received more than twice the usual warning time to seek shelter.

Pamela Heinselman, project manager of the prediction model called Warn-on-Forecast, told Eos that the National Weather Service (NWS) forecasters in Norman saw the test as “significant in terms of being able to put out that advisory and then have confidence to issue a warning…earlier than they would have been able to do otherwise.”

Warn-on-Forecast predicted the 16 May supercell, a type of strong, rotating thunderstorm that commonly precedes tornadoes, hours before it formed in the Texas panhandle. As the program processed real-time weather data, it reported a 90% probability that extreme wind shear and updrafts would form across a swath of western Oklahoma and reach a peak over Elk City.

NWS’s parent agency, the National Oceanic and Atmospheric Administration (NOAA), publicly announced the test of the new model on 13 July.

Turning Predictions into Tornado Warnings

Warn-on-Forecast combines a large number of high-resolution atmospheric convection models with real-time radar observations to generate probability-based forecasting maps. The comparison of modeling results with the ever-changing radar information yields maps that predict the formation and path of severe weather more precisely and with more lead time than current forecasting models allow.

Warn-on-Forecast produces forecasting maps like this 3-hour weather prediction
Warn-on-Forecast produces forecasting maps like this 3-hour weather prediction for the Texas panhandle and western Oklahoma from 16 May. The map shows areas that had 90% probability of severe storm conditions. The color-filled areas depict the worst-case scenario thunderstorm intensity at the time based on rotation and updraft speeds. Red and purple regions are areas where conditions were favorable for tornadoes. The boldly outlined contours, like the figure eight to the right and slightly above the map’s center, indicate the predicted locations of strong thunderstorms at the end of the 3-hour period. The small cross in the center of the purple region shows the predicted location of maximum storm intensity, a spot near Elk City, Okla. Credit: NOAA

Before the Elk City tornado, the software “indicated the possibility of intense supercell thunderstorms capable of producing tornadoes moving from the Texas panhandle into western Oklahoma over the course of [a] 3-hour period,” said Patrick Skinner, a research scientist with NOAA and the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies in Norman.

Researchers from NOAA’s NWS and NSSL working out of the NWS Forecast Office in Norman issued a tornado watch for 33 at-risk counties 90 minutes before the storm. A tornado watch means that tornadoes are possible but have not yet been spotted. Local emergency management then activated outdoor warning sirens 30 minutes before the tornado touched down in Elk City.

Currently, NWS issues a severe weather warning when meteorologists first see a supercell on radar or receive reports of local sightings. This “warn on detection” approach gives the public an average of 13 minutes of advance notice before a twister hits.

Local news outlets later reported that the tornado damaged between 20 and 30 homes and businesses in Elk City, injured multiple people, and caused one fatality. NWS categorized the tornado as an EF2 on the Enhanced Fujita Scale, with wind gusts faster than 179 kilometers per hour (111 miles per hour).

elk city oklahoma tornado
The Elk City tornado damaged businesses and homes like the one shown here, but residents received a tornado warning 90 minutes before it struck. Emergency management activated the outdoor tornado sirens 30 minutes before the tornado struck. Credit: NOAA

Although Warn-on-Forecast’s current 30-minute warning time is a significant improvement, Heinselman explained that her team aims to increase this time to an hour to reduce fatalities and injuries and give high-density locations like hospitals and stadiums enough warning to evacuate.

Beginner’s Luck?

This successful test of Warn-on-Forecast was part of the 2017 Spring Forecasting Experiment at NOAA’s Hazardous Weather Testbed. Warn-on-Forecast was a first-time participant in this annual NOAA event, a modeling-focused experiment coordinated between the Storm Prediction Center and NSSL.

According to Heinselman, experiments like these are critical for understanding the strengths and weaknesses of the forecasting program and for improving the current version of the model. Warn-on-Forecast is still in the experimental stages of development and is not expected to be fully operational for at least 6 to 8 years, she said.

Because the Elk City forecast was the first attempt by NWS forecasters to use Warn-on-Forecast for real-world predictions and storm warnings, the team does not yet know whether the accuracy of the prediction typifies the software’s capabilities or was just a one-time success. The researchers expect to continue testing with NWS. These tests should enable the researchers to “collect more cases with the model, which will allow us to more thoroughly evaluate its performance,” added Heinselman.

Warn-on-Forecast and a related program, Forecasting a Continuum of Environmental Threats, aim to deliver detailed storm predictions across a “threat grid” that updates on the basis of real-time data, Henselman said. Other currently in use predictive models issue a “yes or no” storm prediction for large areas and can have a high level of uncertainty. “From probabilistic-type guidance you can give a more specific area of impact associated with different threats,” she explained. “The goal is to be able to reduce the [geographic] size of that warning based on, in part, model forecasts.”

—Kimberly M. S. Cartier (@AstroKimCartier), News Writing and Production Intern

Citation: Cartier, K. M. S. (2017), Storm model foresaw tornado precursor hours before twister hit, Eos, 98, https://doi.org/10.1029/2017EO078469. Published on 26 July 2017.
© 2017. The authors. CC BY-NC-ND 3.0
  • Reva Madison

    Looks like McLean is at the very extreme Southwest end of that track. I wonder how much time, if any, in advance they were given. With one dead and several injured in Elk City,it appears that one of two things happened: people did not have a storm cellar to go to, or ignored the warnings. As a kid, we spent many hours in shelters, both after the towns fire alarm went off, or on occasion from our own observations and knowledge of weather, Today, living in Virginia, I do not know of one house with a storm cellar, yet the state does get a number of hits each year. I myself observed winds forming a circle above my head, from the back porch of our house. We headed downstairs to the basement. At the same time, my daughter was in town, getting off work, and picking up her kids from a nursery. She drove to her home, the other side of town from us, and coming over a hill, saw a tornado touching down, directly in front of her. She saw an old house, about a 100 yard down a dirt road to her right, and spun into it, rapidly toward the house. The people in that home were on the porch and motioned her and the kids inside. They fled to the basement. A bit later they looked out and the storm had gone on by, but it left a brand new house, across the road, flattened, and then a church and another house, a few hundred yards away, were damaged badly. It was the same storm that I saw, and reported to the national weather service , via ham radio from my basement. So, it had touched down, about 20 miles from where I saw it developing. It would certainly be nice if they could predict these events a half hour ahead of time, or even better, of course, an hour. People still have to pay attention and get to shelter. Its better to spend a few hours in shelter, over the year, than take the risk, thinking “It is just another false alarm”.