September 27, 2006 Southern Illinois Chase

by John Farley

With a rather strong cold front, good speed shear, and some low-level directional shear, it looked like storms would be a good bet on this day, and supercells a possiblity in and near southern Illinois. Moisture was an issue, but strong forcing, shear, and upper support would likely be enough to trigger strong storms anyway. I was concerned that the storms could go linear fast, though. I was thinking of heading down to around the Rend Lake or Carbondale areas to see what would happen. If severe wx were to indeed occur, it would likely be in the same general area affected by the previous Friday's outbreak (Sept. 22), though perhaps just a tad further east.

By 12:30, I was out the door, planning to head to Marion, IL to get decently ahead of the front, then check data to refine my target. I arrived in Marion around 2:30, as planned. I had noticed during a brief stop at a rest area by Rend Lake that a few small CU had formed just north of the lake. Otherwise, there were only a scattering of mid and high-level clouds, with the radar showing a few light showers developing farther north behind the front.

By the time I got to Marion, I noticed the CU to my N and NW had congealed into a line with a few moderate cumulus, but nothing that looked impressive. After a couple abortive attempts to get WiFi, I went to the library where a helpful librarian got me the needed authorization to use the computers there.

Based on what I saw, I was pretty much committed at that point to continuing down I-57 to the Sikeston, MO area. There were no storms in southern IL at that point, and the front, clearly visible on the radar image, was already just NW of Marion, undoubtedly where I saw the CU. There were storms in MO, but they did not look impressive. However, SPC had issued two mesoscale discussions, one roughly from Marion to the SW into MO, and the other for E and NE of there into IN. They thought the greater potential was in the southwestern one. However, the SPC mesoscale analysis page showed those storms moving into an area of reduced instability, with better instability in the area right around Marion. Nonetheless, with the front nearly there already and with poor chase terrain in the Shawnee National Forest south of Marion, the wide flood plain in far SE MO ahead of the storms in MO did seem like the better option.

However, as I got back in my car to return to the freeway around 3:30, I noticed that several storms were in the process of firing to my north, presumably along what had been the line of small to moderate CU. These exploded so quickly that they had not been visible on the radar just a few minutes earlier! Here is a photo of the storms at the time of initiation,around 3:30, looking north in Marion.

I quickly decided that a storm in the hand is worth 2 in the bush, and besides, these storms were going up in an area of better instability than what the MO storms were moving toward. I headed east out of Marion, then turned north on IL route 166 past Pittsburg to a T-intersecton 3 miles north of Pittsburg. Then I went east. It was quite wooded for several miles, no good places to stop and view storm. I had never chased this far south in IL before, and was initially disappointed with the terrain. However, it got better later as I followed the storm east.

Initially there were four distinct storms in a line. However, there was little but blue sky and a small flanking line SW of the southwesternmost (tail-end) storm, and I thought it possible that this would become the dominant storm and that the cluster might evolve into more of a supercell-type structure. This is pretty much what happened. This evolution was well under way when I took this picture of the tail-end storm:

This picture was taken west of Galatia, near the Williamson-Saline Co. line, looking NW into far southeast Franklin Co. The storm went SVR warned shortly after this, at 4:20, for Hamilton Co.

This picture was taken shortly later, looking NW from the entrance to Harrisburg Lake. The storm is in Hamilton Co. now.

After a while longer, a wall cloud - the only really pronounced one that I saw - formed under the updraft, as the storm completed its transition into a supercell structure:

This picture was taken from IL route 34 east of Galatia. The storm had by now produced half-dollar hail in the McCleansboro area, and did so again in the Norris City area shortly after this time.

Here is a zoomed view of the wall cloud. Not too long after this, second SVR is issued, for White Co. Shortly later, at 5:00, when the first waring expires for Hamilton Co., a new warning is issued for the southeast part of the county, near where this wall cloud was observed.

This deer watched me for a while at my next stop, then took off running when I lowered my window for pictures. The deer crossed the road ahead of me. By this time, the wall cloud had dissipated, and the storm was cycling with a new updraft. This was somewhere west of Eldorado. By the time I was approaching Eldorado, the anvil above the updraft had become quite backsheared.

I continued to follow the storm to about 5 miles east of Eldorado, into western Gallatin Co. A new SVR was issued for Gallatin Co. and Posey Co. across the river in Indiana, and the storm produced marginally severe hail in New Haven. This is the fourth SVR warning for this storm, and the last for IL. Two subsequent warnings were issued in Kentucky, however, and the storm kept going for two more hours, producing more hail in several areas as far east as Owensboro. I broke off the chase around 5:20, as the storm was crossing into Indiana and Kentucky.

Looking ESE into Indiana and Kentucky at the supercell storm from southern Hamilton Co. as I return home.

All in all, this was an unusually photogenic storm for Illinois, and a pleasure to observe. I had been expecting fast motion, perhaps again 50 mph like September 22, based on the strength of the mid-level winds, and at first the cluster of storms did move quite fast. But once the tail-end storm became dominant, the process of backbuilding slowed the motion considerably, and the storm moved to the ESE at a very chaseable 30 mph. Perhaps owing to the somewhat lower-than-usual (for Illinois) dewpoint, the storm was rather high-based, which initially made me think it was closer than it really was. However, my eastward route worked well, as the storm moved toward the ESE, bringing it closer but not close enough to force me to turn southward. Total chase distance: around 350 miles.

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