DUNKERTON -- High winds Sunday tore into a fertilizer storage facility under construction at the Dunkerton Co-op and brought new misery to a farmer still trying to rebuild after the devastating EF5 tornado in May.

The blast peaked at 58 mph at the Waterloo Regional Airport, according to Craig Cogil, a meteorologist with the National Weather Service in Des Moines.

Based on other evidence, Cogil said the wind might have topped that speed near Dunkerton.

"The highest gust that we got was up to 65 mph up by Mason City, a town called Ventura," he added.

The steady rush of air severely damaged a $2.5 million project several months in the making at the Dunkerton Co-op. The wind lifted the roof off the new storage facility, tipping two small bins that were not yet anchored and scattering fresh lumber and plywood.

The damage happened between 11:30 a.m. and noon. The co-op hired Marcus Construction of Prinsburg, Minn., to build the structure, which measures 100 by 170 feet. None of the company's or co-op's employees were injured.

"That's the thing that was a blessing. Nobody was working on it," said Harlyn Vander Linden, co-op general manager.

The mishap throws the grain elevator's schedule off, however.

"We were hoping to take fertilizer in a couple of weeks," Vander Linden said. "Now we're backed up a couple of weeks.

As of Monday, an estimate for repairs was not yet available, but Vander Linden noted the co-op has builder's risk insurance.

Cogil said at 58 mph, typical damage would include small-to-medium branches, perhaps even uprooted trees.

"Usually you're not going to have a lot of structural damage to houses," he added.

A few blocks away, the Kwik Star in Dunkerton lost its main sign about 12:30 p.m. The 8-by-12 sign blew out of its frame and lightbulbs inside shattered.

"The wind was just blowing so hard," employee Jo Bokemeyer said.

Scott Segebarth of rural Dunkerton was harvesting at the time.

"They said 58 mph, but in my estimation it was closer to 70," he said.

Though his Gleaner combine was full of corn, Segebarth could feel the wind's force.

"The combine was rocking to the point I thought I shouldn't be out here, and that doesn't happen very often," he said.

The tornado in May severely damaged Segebarth's home and farming operation on East Mount Vernon Road. Sunday's winds knocked down as much as a third of a field of corn, and a nearby elevator leg being reconstructed for Willard Frost toppled once again.

"We can't win," Segebarth said.

Some buildings under construction in Parkersburg also took a hit, said Virgil Goodrich, the city's economic development director. The town is experiencing a wave of repairs and new construction after the tornado tore through the community's south side last spring. That storm also killed eight people in Parkersburg and New Hartford.

A business plaza going up lost part of a framed wall, he said, and the wind blew away roofing material elsewhere in town. However, the recent damage appears to be minimal and should be easily replaced.

"It's kind of mild compared to what we had on the 25th of May," Goodrich said.

Contact Dennis Magee at (319) 291-1451 or dennis.magee@wcfcourier.com.