April 5, 2010 chase BUST

by John Farley

This was a painful bust. Models were showing a good combination of instability and rather extreme wind shear along a warm front in northern MO. However, they also were not breaking out a lot of precipitation, and capping was a potential issue that could prevent storms from forming. It was the kind of day where the storms would be spectacular if they developed, but they might not develop at all, resulting in a blue sky bust. The warm front also continued eastward across IL, but the models were predicting better instability farther west, closer to the triple-point low in northeast KS or southeast NE.

With storms likely to develop by 4 p.m. if they were going to, I needed to leave by about 1:30 if I wanted to chase in northern MO. I targeted the general area bounded by Bowling Green and Quincy westward to Kirksville. When I stopped for gas in north St. Louis County (I-270 and Lilac) about 10 miles from home, I noticed a pretty little shower (I call it that because it did not yet have thunder and lightning, as far as I could tell) moving northeastward a mile or so west of the gas station. It rained a little at the station, but a very localized burst of heavier rain could be seen a mile or so west. I thought it had pretty structure - definitely the precipitation was nicely downshear from the updraft, which had a round, hard base. It even formed a couple small lowerings that I would have called wall clouds if I had a real storm, not just an isolated shower.

It looked interesting enough that I considered chasing it, and could have, by heading north on route 367 and crossing back into IL at Alton. But doing so would have eliminated any chance of getting to my real target area by the time storms were expected to initiate, so I did not. Instead, I hooked up my computer so I would have radar, and blasted west. I was encouraged by the formation of a new storm near Warrenton, figuring that the cluster of showers and storms near St. Louis would expand westward along the warm front (now draped about across the St. Louis area) and lead to good storms in my target area. But by the time I reached route 61 to turn northwest toward my target area, the Warrensburg storm had died out, leaving just a small cluster of cumulus clouds in the general area where it had been. Soon, I was in an area of clear, blue skies, and that's where I would stay the rest of the day.

Meanwhile, the shower near the gas station had turned into a severe-warned thunderstorm in northern Madison County, IL, and it went on to produce the only daytime tornado of the day in the United States, near Hillsboro, IL. That is about 40 miles from my home, but 100 miles east of where I was by then. There were other storms in IL, too, by now. I gave up on the MO target when I got to Bowling Green, and headed back east into IL through Louisiana, MO, but by now I was too far north and west and before I could get near them, the storms died out as the energy shifted eastward into Indiana.

What went wrong? Well, I knew, as did other chasers, that the northern MO target might be a blue-sky bust, and it was. But what I did not know, because the models badly missed this part, was that the best instability developed in southern Illinois, not northern MO. By the time of the tornado, CAPE in southern IL was around 2,500, while it was under 2,000 in the northern MO target area - just the opposite of what the models predicted. So the models were right about little or no precipitation in nothern MO, but wrong about where the best instability would be. I would have been much better off chasing the "shower" I saw at the gas station. Probably 4 times out of 5 that would have been the wrong thing to do, but today it would have worked out much better. I guess that's what makes storm observation such a challenging hobby. One thing I probably should have paid more attention to was that before I headed out, instability was already greater in southern IL than in MO - CAPE around 1000 in southern IL, less in MO. But the area of instability was expanding, and I figured the bright sunshine moving into northern MO would ultimately destabilize that area more than southern IL. Wrong.

Total chase distance: 300 long, frustrating miles.

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