On Friday July 25, 1997 I was a weather observer at the Dane County Regional airport in Madison, Wisconsin. Around lunch time thunderstorms rolled through the Madison area and produced substantial rainfall. By 3 pm (the start of my shift) the skies over Madison cleared as temperatures surged into the lower 80s and dew points were in the mid 70s.
The Storm Prediction Center had issued slight risk for all of Wisconsin on this afternoon but due to a strong capping inversion (Temperatures at the 850mb level ranged from 22 to 26 degrees Celsius) most local meteorologists had forecasted a warm and humid but quiet evening for the Madison area.
4:30 pm CDT: Stratocumulus bands began racing to the northwest at about 1500 feet above the ground.
5:30 pm CDT: A band of altocumulus castellanus appeared overhead.
5:56 pm CDT: Hourly Observation: Temperature 85 Farenheit, Dew Point 79!.
6:15 pm CDT: Scattered towering cumulus had appeared along with a west to east band of cirrostratus, (an upper level jet max!)
6:30 pm CDT: All the towering cumulus had vanished, off to the west was one exploding tower with grooves on its lower portions, the storm was beginning to organize, 5 minutes later I heard the first rumble of thunder so I went inside to issue a special observation for a thunderstorm at the airport.
As I started to head back outside when one of the air traffic controllers (I was in the Controll Tower Building) asked me if we were going to have a tornado. I was puzzled and I said, no one forecasted it but we certainly have the wind shear for it! I then went outside and was somewhat stunned: to my north was a large, round dark blue storm base.
A brief funnel cloud appeared at about 7pm CDT.
This new wall cloud exhibited rapid rising motion but it was not rotating and it soon disippated.
Heavy rain set in for about 20 minutes, local radar showed the next large storm just to our northwest and it was moving due east. I went outside with several air traffic controllers to watch the sky as this main storm was going to pass just to our north. After the rain stopped around 8:15pm CST we could see mammatus clouds to our west and a grey area to our northwest. over the next few minutes dark bands began to appear in the haze and soon this massive rotating updraft (below) was moving toward us.
Cloud to ground lightning strikes were coming from the lower portion of this cloud. It quicky became apparent that we needed to seek shelter in the control tower building. Before we got inside there were 2 lightning strikes within 1 mile of our location. The Air Traffic Controllers on duty evacuated the tower cab when they saw a funnel under this cloud that extended down to the tree line (at the bottom of the picture above). After transmitting the special observation for the tornado I went outside and to our north was the mesocyclone which was the most rapidly rotating cloud I have ever seen. Leaves were being blown off the trees as this circulation passed over them. The clear slot wrapped around the mesocyclone before the circulation finally disappeared. Naturally my disposable camera was useless at this point because it was now 8:40pm CDT and we were losing light fast. Tornado sirens were wailing for much of the evening around the Madison area but no other tornadoes were confirmed after dark.
CIMSS has a good analysis of this
event you can see it by clicking here.
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