On radar, the thunderstorm appeared to be weakening.
It had been hours since the storm produced two brief, weak tornadoes in Reno County, and spotters reported no signs of funnels as darkness shrouded the Kansas plains Tuesday night.
Because rotation in the storm appeared to be weakening, forecasters in the Topeka branch of the National Weather Service chose not to extend a tornado warning for Morris County into neighboring Wabaunsee County.
That meant the only tornado siren in tiny Harveyville was never activated, and the town was hit without warning.
“The radar didn’t show rotation until it was directly over town,” said Chad Omitt, meteorologist in charge of the weather service’s Topeka branch. “It just makes us sick.”
The tornado, rated an EF-2 with maximum winds of 130 mph, killed one person and injured at least 11 others in Harveyville. An estimated 40 percent of the town of about 250 was damaged or destroyed by the tornado, which was on the ground for about five miles and was at most 150 yards wide.
It touched down a mile southwest of Harveyville and raced toward the town at 60 mph. That meant it struck the west side of town in less than a minute.
“It was a rain-wrapped tornado – at night,” Omitt said. “Nobody would have seen it.”
Four minutes before the tornado touched down, the private forecasting service AccuWeather issued a tornado warning for two clients in the area: Westar and the Kansas Turnpike Authority.
“We were watching that cell because it had been persistently having tornadic signatures,” said Mike Smith, senior vice president for AccuWeather Enterprise Solutions, based in Wichita.
Along with producing two tornadoes in Reno County, the cell had strengthened over Marion and Chase counties to the point that the Wichita branch of the Weather Service issued a tornado warning that included the caution: "The potential for a large tornado is high!"
Strong thunderstorms typically rely on the atmospheric instability fed by sunlight and weaken after sunset. But meteorologists said this storm was able to stay strong – and even intensify – at night because there was so much wind shear in the atmosphere that night. Wind shear is the amount of rotation in the winds at various levels.
Strong wind shear can create favorable conditions for tornadoes even when other ingredients commonly connected to twisters may seem insufficient, Omitt said. It can also mean that small tornadoes, such as the ones that hit Harveyville and Harrisburg, Ill., before dawn on Wednesday, can nonetheless be powerful.
“It’s capable of producing very intense, very small tornadoes,” Omitt said. “These are the types of storms that are extremely difficult to detect.”
Damage assessment surveys have revealed six tornadoes touched down in Kansas on Tuesday – four more than initially thought. Two were northwest of Concordia, not far from Belleville.
Had his office received those reports that night, Omitt said, meteorologists in the Topeka office likely would have issued a tornado warning for the storm that eventually struck Harveyville because the reports demonstrated the system’s capabilities.
“It was not an easy night, that’s for sure,” said Darrel Smith, information technology officer for the Topeka office.
Weather service officials in the Topeka office are conducting a review of the data collected and decisions made Tuesday night.
“You do that with every event,” Smith said. “‘What did we do wrong? Did we miss any signs?’ That will continue on for the next several weeks.”
One of the most difficult aspects of the Harveyville tornado was how quickly everything happened. The storm went from looking like a thunderstorm morphing into a long line of storms in one radar scan to producing a tornado that was hammering Harveyville in the next scan four minutes later. One the next scan, the tornado was gone.
“Events like this bother the heck out of us,” Omitt said.
Among the lessons of Harveyville, he said, is to give more weight to what strong wind shear is capable of.
Smith said he doesn’t fault the meteorologists in the Topeka office for their decisions. They were hampered by the slow radar scans. Branches in Kansas City and Wichita have access to high-resolution radars used by the Federal Aviation Administration, which scan much more often, he said.
For areas that can’t be covered by the high-resolution radars – such as Harveyville – the Weather Service should adjust branch radars so they scan more frequently than every four minutes, Smith said.
“We do know how to make the radars run faster and get more data and not miss things like what happened in Harveyville,” he said.