Weather service confirms: Yes, it was a tornado
According to Todd Krause, weather warning coordination meteorologist for the National Weather Service, Saturday evening's storm spawned two tornados in St. Croix County, one just north of Hammond and the other northwest of Burkhardt.
Sunday, by the time Krause completed his survey of damage in the western Metro area, it was mid afternoon when he headed for St. Croix County.
"We had two known areas of damage that we knew about," said Krause. "One of our weather spotters called in a location 4 miles north and 1 mile west of Hammond, and we had reports of the damage near Burkhardt. You can't just drive around blindly looking for damage. In both cases we had specific locations."
Krause headed to Hammond first and made his way back to the Town of St. Joseph arriving at Oakwood Lane, close to sunset.
"I was driving west on County E when all of the sudden I started seeing trees down near the Three Lakes area," said Krause. "I started scanning and kept on seeing stuff north of where A and E come together."
The tornado path was 5 miles long and ¼ mile wide, starting just west of 60th Street and continuing to just west of the Three Lakes.
According the Krause it likely was a multiple vortex tornado.
"It is one parent wide circulation, I like to compare it to the Tilt-a-Whirl ride, while the ride is going around there are little swirls going around the periphery," said Krause. "It is very likely it was a vortex tornado, with lots of individual mini tornados. It is actually pretty common especially given this was a very strong storm."
A second phenomenon was also evident to Krause as he surveyed the storm damage.
"One of the interesting things that we have learned about storms is that a secondary cause of damage is the rear flank down draft," said Krause. A lot of the trees were broken off several feet above the ground with little twisting indicating this second cause of damage.
"It is a descending column of air that comes from a corridor of wind circling around the backside if the tornado," said Krause. "That air can be up to 100 mph. It sometimes looks like it was all tornado damage. That is why you see such a wide damage path."
"There was plenty of tree damage, the tornado was ¼ mile wide and on the southern end you could see the effect of the downdraft."
According to Krause, the tornado north of Hammond wasn't as strong but it was definitely there, only one house partially lost its roof.
The hardest hit areas in the Town of St. Joseph included significant structural damage reports on Oakwood Lane, Walsh Road, Beatrice Circle and Bass Lake Road. While acres of wood lots and corn suffered significant damage as well.
See the August 13th print edition of the Hudson Star-Observer for more coverage and photos from the storm.