Gilbert Sebenste's 7/19/95 Iowa Storm Chase

Well, SELS day 2 on the 18th at 18Z said it all. A moderate risk for severe thunderstorms for northern IA confirmed my suspicions after I had taken a look at the morning runs off of DiFAX. By the afternoon of the 18th (Tuesday), I had already lined up a partner, Karl Schulze (soon NIU weather director). After he had looked at the gridded data from the ETA/NGM, he admitted it looked pretty good for July. We made plans to meet at my TV station at noon Wednesday.

Wednesday came and things were still looking good. In fact, the 850 MB chart at 12Z showed a strong shortwave in far western IA, which still showed up well and even stronger than the models. This coupled with a warm front in the area providing southerly winds and good inflow, nearly westerly 500 MB winds, and good heating led me to believe IA was the place to be. But where?

Well, Karl had to make a run to the vet with his dog, and he got up here about 1 PM. That was OK, since I wasn't sure where to go yet. But when the 1 PM obs came in, it became clearer: Showers and a few storms had started to fire ahead of the shortwave axis. Moreover, Lamoni (30I)'s ob had TD's in the mid 60's, and climbing. DSM was 86/62. A southerly strong LLJ was now being seen across east central IA. When Karl arrived, we decided to head for Iowa City, our "target town".

Okay, we probably took a roundabout way, but at 1:45 PM, we left and took I-39 to I-88; we then took my car (had AC and better gas mileage!) to I-80. But we had lost time, despite smooth Interstate travel. Still, we had plenty of heating, daylight...and hope.

But, things weren't perfect. Karl's cell phone, to our dismay, had a short in it. If you held it at certain angles, it cut the power...and your call. Twice we tried to call for information, but were denied as he struggled to figure out where the problem was.

At 4 PM, we got on the Mississippi river bridge on I-80. The speed limit was TEN mph, due to construction on the bridge. As we were halfway across, Jeremy Hylka at the College of Dupage rang. There was a tornado warning for Grundy county IA! At first, Karl thought he was kidding. (Actually, Jeremy was late on that one, but caught the next warning for Tama county, which was in effect then). All we could do now is hope that was an isolated storm or tail-end charlie, as we zipped across IA towards Interstate 380. COD had lost their radar data feed.

By 5 PM, we hit 380. We quickly refueled and headed north on 380 and saw the storm. What awesome hues of green! A group of SKYWARN amateur (sounded VERY professional and organized) radio spotters were calling in to a central location, which was telling everyone on that frequency to stay off unless you were reporting severe wx. We decided to take the road just south of the airport and see what it would do. We followed it east to Ely, where the warnings were cancelled and the storm began to look like crud. In dismay, we headed toward Iowa City again to eat a quick lunch that we never had, and to hope the line would build south.

But as we left, apparently, since I don't have the radar from the event (Eric Helgeson, care to chime in?), the following happened: The line, about 20 miles east of Cedar Rapids, re-intensified, bowed out, and then produced a "doppler indicated" tornado 20 miles southeast of Cedar Rapids at 5:44 PM. At 5:45 PM, two chasers in a Hardee's parking lot looked at each other in total disbelief. "That line of storms stunk, what the....?"

Well, thank goodness I was on my last gulp of my drink as I tossed the empty container in the back seat, and headed WEST toward I-80 (it was only a mile...or go thru Iowa City again). We went east on 80 and caught up to the line a half hour later on the interstate...in southern Cedar county. No tornado. But visibility was lousy due to the heavy rain, and I knew we had to break out of it. Finally, in Scott county, we did, as a severe thunderstorm warning was now in effect. But with the line accelerating eastward, we knew the only way we'd catch the bow was to get to IL first. Fortunately, the speed limit on the mighty Mississippi river bridge was now 45...and we crossed it in MUCH less time than going the other way!

But then...the "Illinois Jinx" struck again! :) The line ran into stable air...and died literally in 20 minutes as it crossed into IL. The only two showers left after that were on the far northern and southern edges of the bow. At 7 PM...it was all over.

As far as I can tell, several things happened that prevented us from seeing the big wedge. Although the LLJ was strong, the axis was narrow, and when it hit the air in IL with TD's only in the 50's, it ran into more stable air. It also obviously outran the inflow, and the shortwave which kicked it off. And since the warm front had become very diffuse, the surface focusing mechanism was gone, despite reasonable helicities and upper level wind shear and support to produce severe weather and tornadoes.

Gilbert

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Gilbert Sebenste ********
Internet: sebenste@geog.niu.edu (My opinions only!) *****
Owner of the Storm Chaser Homepage ***
URL: http://www.stormchaser.niu.edu/chaser/chaser.html **
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