4-11-2001 - Small Tornado west of Iowa City, Iowa.

By Chris Gullikson

Synoptic setup.

A powerful negative tilt upper-level trough was moving NE out of the SW US towards Kansas. A deep surface cyclone had developed over western Kansas and would move quickly NE into NW Iowa by evening. At 17Z, a cold front was located from eastern Nebraska thru west Missouri. A warm front was located across central Iowa extending east. Very strong, SW unidirectional flow from 700MB and up was entering SW Iowa and triggering convection out ahead of the cold front in SW Iowa and NW Missouri. A low level jet was forecasted to intensify and enter southern Iowa with 60 knot winds from the south. A rapid clearing trend in NW Missouri from the upper level dry slot would quickly erode a cirrus shield over northern Missouri and southern Iowa. Dewpoints over southern Iowa were in the low to mid 60's with a dewpoint axis noted from central Illinois into east central Iowa where low level flow was most backed.

The chase.

This was a highly anticipated day as the powerful upper level trough would bring great dynamics for tornadic storms into Iowa. SPC had a moderate risk for Iowa on early Wednesday, but was considering changing to a slight risk due to lack of heating over southern Iowa. Visible satellite imagery verified a dense cirrus shield over all of the upper Midwest. I was pessimistic at this point about individual cells being able to develop without some surface heating and thought it would be a squall line event just like the April 6th event in SW Kansas last week. Talking with Doug Raflik, I decided to hang out at home until the new Day 1 Outlook was issued at 16:30Z. Doug left Waupon at 10am with plans to head towards Waterloo Iowa. At 16Z, the SPC had issued a Mesoscale Discussion for Central and Eastern Iowa concerning tornadic storms. The 16:30Z Day One had the Eastern third of Iowa under a high risk with the tornado probability at 25% over eastern Iowa into Illinois. Thoughts of another high risk bust definitely entered my mind but I was getting excited nonetheless. A PDS watch box was issued for central Iowa just before I left at 17Z. I called Don Lloyd just before I left to update him on this rapidly developing situation, he was already 20 minutes in front of me heading towards Iowa. (Thanks to Stan Olson for the SPC product archives)

I left Madison WI about Noon local time heading towards I-88 in Central Illinois to get on I-80 into central Iowa. My target at this point was Iowa City. I called one of my chase friends, Scott Weberpal and picked him up on my way thru Janesville.

Doug Raflik reported clear blue skies as he was approaching Cedar Rapids Iowa with towering CU's in the distance. Don Lloyd verified that the cirrus shield was eroding as he was entering into Iowa. We experienced a brief clearing of the skies once we got into Iowa but the 850 low level jet quickly brought low level clouds over us, completely ruining our visibility.

After conferring with Don and Doug by cell phone, we decided to head west of Iowa City along I-80 to intercept the line of individual storms that were oriented in a NW/SE line. Kinney Adams was Nowcasting for us and told us the storms were going tornadic as they crossed into southern Iowa, approaching the warm front. He advised we drive out to the storms along I-80 then drive east to look at each storm as it raced towards us at 50+ MPH from the SSW.

Scott was navigating and watching radar on a local TV station. The radar was showing a tornadic storm over Ottumwa IA that looked to be in a good position to intercept. We dropped a few miles south of I-80 and positioned ourselves on F52, a east/west paved road. We drove back and forth between Parnell and Holbrook watching radar and trying to see where the foward flank precip core was. My plan was to be just east of the rain core and let it pass then drive west to see the base of the storm. As luck turns out, we spied a clear slot between 2 precip cores and just let the clear slot ride over us.

As the the clear slot came overhead, rain curtains were observed moving to the SW, as if we were in a RFD, which it turns out we were. A rain free base could be observed to our south as the rain slacked off and a faint lowering with a funnel was observed. As the rain continued to slack off, it became quite obvious that we we looking at a small funnel cloud that would briefly become a tornado then quickly rope out before crossing F52. This event started at 4:45pm CSDT and lasted for 3 minutes.

We headed east on F52 with the idea to catch the next storm coming up from the south. I called 911 to report what we had seen then called Don and Doug to let them know about this storm. Doug was up on I-80 and was able to position himself west of the Oxford exit to see the funnel cloud pass over the interstate at 5:05pm. Don was on the storm to the NW and from what we could see, it looked more impressive then the storm we were on. (The storm Don was on is to the left, the storm to the right was what had just produced the tornado)

As we drove east on F52, we could see another funnel from the same storm so we headed north on W38. The funnel was several miles away at this point but we able to observe it as it went over I-80 and Oxford. We eventually lost site of the funnel north of Oxford as we lost a good north road to follow.

Driving north-east on 151, we came up on a rain free base with a long flanking line just before entering Cedar Rapids. Doug called and said this storm had a tornado warning on it and he thought he could see a funnel at times from his location to the north of me. We were able to get east and along side of this storm but it became elevated with a linear base as it moved north of the warm front and across the Mississippi river into WI. (22:15Z satellite image after storms moved through)

I feel fortunate seeing anything with this kind of a system. It made up for the 2000 mile bust in SW Kansas on 4-6-01  last week that just produced a squall line in a very similar setup as today. Ironically I saw my first tornado just 20 miles to the east of this one while chasing with Stephen Jascourt on May 15th 1998. We intercepted that tornado just like this one, watching radar on local TV and positioning ourselves on a east/west road. The visibility was terrible that day and the storms were moving at 50 plus.

Chase Distance - about 600 miles.

Links

4 Meg Video Clip - accelerated 600%

Scott Weberpal's video pics

Doug Rafliks pictures

Stan Olson chase account

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