The violent, long-lasting and deadly tornadoes that struck northern Arkansas on Sunday were, by and large, well-forecast, according to data from the National Oceanic and Atmospheric Administration. In fact, if forecasters erred in any respect, it was in thinking that more tornadoes would form than actually did touch down in the end.
The hard-hit town of Mayflower, located about 17 miles northwest of Little Rock, had about 30 minutes of lead time between when the tornado warning was issued to when the town was hit, according to John Ferree of the Storm Prediction Center (SPC) in Norman, Okla. This was well above the national average tornado warning lead time of 13 minutes.
Ferree told Mashable in an email that Vilonia, Ark., which also sustained heavy damage with tornado-related fatalities, had about 21 minutes of warning lead time. However, since Vilonia is located about 15 northeast of Mayflower, residents of the town had a lot longer, closer to 50 minutes, to prepare for a potentially damaging storm headed their way, Ferree says. Still, finding adequate shelter to protect against a violent tornado on the high end of the Enhanced Fujita Tornado Damage Scale, which the Mayflower and Vilonia tornadoes likely were, can be difficult.
The tornado that struck Mayflower was likely not the same tornado that hit Vilonia, according to the National Weather Service forecast office in Little Rock, but both tornadoes came from the same thunderstorm. Forecasters are surveying tornado damage on Monday to determine the details on which tornadoes struck where, and how strong they were.
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Some social science research has shown that when people have much more lead time than usual, they may not take tornado precautions that they would take if the warning were of a more hair-trigger variety, since extra time provides an illusion of safety or can encourage complacency.
Not only were the Arkansas warnings issued well ahead of time, but hours before the storms spawned the deadly tornadoes, the SPC had put Arkansas residents on notice that strong tornadoes were likely to occur in parts of the state by issuing a “high risk” tornado outlook, which is the highest alert category. The SPC had initially outlined the state in the “moderate” risk category for seeing severe thunderstorms and tornadoes, but upgraded part of the state after reviewing more weather data.
Interestingly, the tornado that struck Mayflower began on the northern edge of the high-risk zone, and quickly moved away from it. No other tornadoes touched down in the high risk area, according to SPC data. Carbin said the storm system actually “underperformed slightly” compared to what forecasters expected, which was a larger number of tornadoes. “It wasn’t what I would consider an outbreak by any means,” Carbin says, adding that the final number of tornadoes that touched down will probably be about a dozen, once any duplicate reports of the same tornado are taken into account.
While the Arkansas tornadoes were accurately forecast, a tornado that caused a fatality in Quashaw, Okla., earlier on Sunday did not have a tornado warning associated with it when it hit that community. It did, however, have a severe thunderstorm warning that contained the language, “tornadoes can develop quickly from severe thunderstorms,” Ferree says.
A tornado warning was issued as that storm moved toward Baxter Springs, Kansas, where it caused significant damage, Ferree said.
In addition to the tornado warnings, which are issued when dual-pol Doppler radar data detects intense rotation in a storm or tornadoes are spotted by observers on the ground, the severe weather outbreak on Sunday was highlighted much earlier in SPC’s outlooks. The center showed the possibility of severe weather occurring on Sunday as early as April 21, according to Greg Carbin, a meteorologist for the SPC. This provided the media with six days to drill home the message that severe weather was on its way after a long period of relative calm. “The signal was there six days out as far as outlooks went,” he told Mashable in an interview.
Improved understanding of what makes tornadoes form, as well as more advanced computer modeling techniques, helped forecasters provide greater advanced notice that Sunday would be a risky day across the midwest and south central states. “We’ve seen improvements in longer-range forecast guidance,” Carbin says.