The National Weather Service now estimates top winds of between 170 and 175 mph in the tornado that swept across northern Wood County and entered western Ottawa County late Saturday evening, placing it in the second-highest rank on the Enhanced Fujita Scale.
The decision to "upgrade" the tornado from "EF-3 or higher" - the preliminary rating the weather service assigned the twister on Sunday - to EF-4 was based on a survey team's study Monday of damage to buildings along its path, said Gary Garnet, the warning coordination meteorologist at the agency's Cleveland office.
"I was suspicious on Sunday that it had winds that strong," Mr. Garnet said, which was why the "or higher" was appended to the initial report.
But the EF-4 determination wasn't made until experts were brought in from other National Weather Service offices to confirm the observations.
So far, the weather service has not confirmed any other tornadoes that evening east of Toledo, although wind-related damage was reported in two other areas of Ottawa County besides the track that the deadly Lake Township twister took after slamming through Millbury.
Mr. Garnet said wind damage reported along Williston Road, also known as State Rt. 579, certainly came from the same thunderstorm that spawned the confirmed tornado, but it was undetermined if straight-line winds or another, smaller tornado were responsible.
And the weather service had no firm plan to send anyone there to make definitive observations, he said.
"Our resources are a little light on that," Mr. Garnet said, adding, "We'll make every effort to get someone up there," but that might be through a request to Ottawa County emergency-management officials to do so on the weather service's behalf.
Beth Koch, an administrative assistant with the Ottawa County Emergency Management Agency, agreed that there had been wind damage along Williston Road, although "nothing to the extent of what you see on Trowbridge Road," where an estimated eight homes were destroyed, three were heavily damaged, and 10 sustained minor damage.
Ms. Koch said she was unaware of any request from the National Weather Service for storm assessment along Williston.
Storm-related damage to trees and buildings also was reported near Genoa, Ohio, near the Ottawa-Sandusky county line.
The thunderstorm that spawned the Wood County tornado had earlier produced a destructive twister that formed in southeast Fulton County and dissipated in the Oak Openings area west of Toledo Express Airport in Lucas County.
A map that the weather service posted on its Web site shows the Wood County tornado's course. It started near Oregon Road and I-280 at about 11:20 p.m. and gained intensity as it proceeded east-northeast across the hamlet of Moline and the two railroad yards on either side of that community.
By the time it reached the Lake Township administration building and Lake High School, it packed winds in the high end of the 135-mph-to-165-mph range for an EF-3 rating, according to the weather service.
The twister took a slightly more northerly course after crossing I-280, heading for the northwestern part of Millbury, where it is estimated to have reached its peak EF-4 strength.
Meteorologists estimate tornadoes' wind speeds by reviewing radar data and, in the field, by studying their impacts on trees, buildings, and other objects.
The stronger a tornado, the greater its ability to rip through well-built structures and move heavy objects like cars and appliances.
"Basically what we're looking at is the buildings," Mr. Garnet said. "We study the damage and compare it with structural engineering models. The trees are not a reliable indicator of the damage."
An EF-4 rating was given to the tornado's path in Millbury "due to the large amount of homes that were destroyed down to the foundation," he said.
Mr. Garnet said a wooded area east of Main Street caused friction that briefly weakened the tornado to an EF-2, with winds gusting below 135 mph, but it regained EF-3 strength as it swung due east and then southeast along Trowbridge Road in Ottawa County's Allen Township.
Then it quickly dissipated, with damage suggesting winds of less than 100 mph northwest of Clay Center before it lifted off the ground entirely, according to the map.
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