On the afternoon of June 1st, 2010, I observed a funnel cloud violently rotating about 1 mile north of the Mankato, Mn. airport. The storm had been given a severe thunderstorm warning, but no tornado warnings were issued. The funnel lasted approximately for one minute, so the likely reason no tornado warning was issued was because the rotation that I observed did not last long enough to be seen by radar observers. This is one reason why it's important to have human spotters on the ground: human eyes can see things that Doppler radar cannot.
The following picture was taken from the entry way to the Mankato, Mn. airport at about 1:45 PM on June 1, 2010. I had observed rotation in this storm within 5 minutes of taking this picture (click on the picture for a larger version). I the picture below, I am looking north and that is County Road 12 - aka "Airport Road" - on my left. That is the Hiniker construction building on the left of 12 and about 1/3 of a mile north on this location. The wall cloud is approximately 1.5 miles north of my location and about 1.5 miles west of Lake Washington.
Since I had seen rotation in the storm, I decided to chase after it. I drove north on County Road 12 until I saw the funnel. I pulled over on T-309 - aka 240th lane - a road that runs adjacent to the north boundary of the airport. This funnel was violently rotating, but, I never saw evidence of debris swirling on the ground..
Quickly, the funnel became consumed by the storm's rain shaft, and dissipated.
I chased this storm for a little while longer, hoping to see another funnel. I went south on 12 and then east onCounty Road 26 along the north shore of Eagle Lake. I observed no more rotation, but there was a lot of rain. I didn't feel much like messing with a rain-wrapped tornado or any hail, so I buggered off to the south down County Road 27 and away from the storm. Besides, it was time for me to pick up my kids from school. Family before pleasure.