One storm proved to cause quite the problem across SE Minnesota on Thursday. Over the span from about 4pm through 7pm, the storm evolved into a potent bow echo, cutting from Mankato, ESE towards Preston. Along the path, widespread wind damage due to winds gusting between 45 and 75 mph and one brief tornado.
Here's a look at the reports. The blue dots denote areas with strong wind gusts. The dots that have the broken tree inside denote areas with wind damage. Please know, there are likely countless other spots that experienced wind damage along the path, not necessarily plotted here.
Click the image to see how this storm evolved across our area.
While there were notable areas of damage in towns such as Preston, Racine, Hayfield, Blooming Prairie, and Austin. Reports of numerous large trees downed by high winds, a few communities had damage done to structures by trees falling into them. Just west of Racine, a dairy barn was leveled by wind. Some of the pictures of damage from across our area can be found by clicking on the following picture.
One town particularly damaged was Hollandale. That's where there also happened to be a brief tornado amongst the powerful straight line wind.
Several residents tipped us off to the possibility of one passing through. After looking back at radar data, there was a bit of a signal that a weak tornado may have occurred. A look at the radar imagery from around 4:34pm, shows there was a definite notch on the leaded edge of the developing bow echo, set up right over the town. Velocity data showed a small but still noticeable couplet with gate to gate shear around 65 mph.
After talking with an ABC 6 viewer, Angie O'Connell, who provided me with a wealth of detailed information and pictures. I wanted to take a peak at one location on the west side of town myself. Right on the towns western edge, in a corn field, corn stalks were laid down for a path a few hundred feet long. But instead of the stalks laying down in the same direction there was an element of curvature as you can see in the photo below. That curvature extended back WNW through the field along the path.
Add in extensive damage to small grove of trees immediately at the end of the path through the corn, taking into the account of the orientation of the damage, the signal was there that a brief tornado had occurred.
With all the evidence, I worked closely with the National Weather Service - Twin Cities office for a few hours Friday afternoon, ultimately determining, the confirmation of a brief tornado came down this evening. The NWS rated this tornado an EF0, with a 1/8 mi. length and winds in the range of 65-75 mph, likely lasting less than a minute.
The tornado was not the cause of all the damage across town and was likely only confined to the western side. Looking at other storm damage myself across other parts of town, I saw no evidence of a tornado. These other areas of damage were caused by microbursts, localized strong downdrafts of wind, fanning out across the ground. We commonly call this straight line wind damage.
For more on a recap of the events surrounding this storm, please read up on the blog post by the National Weather Service - La Crosse.