"May Day Surprise" (May 1, 1998) Macoupin County IL Chase by John Farley

Well, today was one of those days when you kind of hope for an interesting storm but don't really expect it. I didn't really analyze weather much, because a quick a.m. check revealed no SPC risk area anywhere near the STL area - we were barely in the "general thunderstorm" area this morning, though that got expanded later. Similarly, TWC didn't even have our area in the "strong thunderstorm" area. So I went no further, but did occasionally check radar through the day - my experience told me that sometimes with a cutoff low to our east, we do get strong storms, if we are right on the back edge of the circulation and if the sun heats the air enough.

By 2:30, I noticed there were quite a few strong storms in central IL and eastern IA - but no warnings. As I made a short drive through town, I noticed clearing to our north from the showers we had been getting much of the morning and early afternoon, and far in the north, a pretty impressive-looking storm - hard tower with anvil extending both E. and W. I figured it was somewhere this side of SPI, but when I got to my office and checked radar, it turned out to be farther away than that - W or SW of Lincoln. But from about 3:00 to 5:20 I holed up on the computer doing work stuff, paying little attention to weather. Somewhere toward the end of that time, I checked radar again and saw that the storm had moved S. to the NW corner of Macoupin Co., and there were a lot of other strong storms in W. IL and E. IA, too - but still no warnings, no SPC risk area, no watch, no nothing.

As soon as I walked outside, however, I was struck by the structure of the storm, whch had now persisted for over 2 1/2 hours - rock hard updraft tower, anvil backsheared to the west and drifting way off to the SE - in any other situation, I'd have thought, "awesome supercell." It still looked good when I got home, and had to be within 30 miles or so, so I grabbed the cameras and Illinois Atlas and headed out around 5:40 - still no watches or warnings. But within 10 minutes, a severe T-storm warning went up for central and southern Macoupin Co. until 6:30 - storm headed for Gillespie. This was based on a spotter report of a severe storm near Carlinville.

The storm continued to look very impressive as I headed up I-55, west on 140, then north on 159. I figured to try to approach it from the S or SSW - it was moving to the S or SSE rather slowly. By just south of Bunker Hill, I saw the first RFB and what looked like a small lowering, both to my NNE. I passed through town in slow traffic, got to route 138 about 2 miles N of town, went 1/2 mile east, and sat, watched, taped, and photographed for 20 minutes, beginning around 6:15.

For a "no risk" day, it was quite a storm. Persistent lowering under the upstream (NNW) side of the updraft for at least 30 minutes - showed the structure of a wall cloud most of that time, though it grew and shrank several times, looked like it was going to occlude once, and was accompanied by various scuddy lowerings. There was quite a bit of CG under the lowering and in the rain and hail shafts to the SE of it. There were several very evident hailshafts. And just behind the lowering for a while was a very dark rain shaft. Eventually, this outran the lowering. As the storm was getting farther east, I moved ahead a half mile to 1200E and went a mile south. This was around 6:40. The lowering grew again, and there may have been a couple very brief needle funnels around 6:45 - or they may have been scud. They seemed to drift north against the southward motion of the storm, but neither lasted more than about 30 seconds. Around this time there also seemed to be a small RFD notch forming just northwest of the lowering.

The storm moved farther south and seemed to weaken, so I decided to head east behind it on the road that runs from Bunker Hill to Staunton to see if there was evidence of severe weather having occurred. When I crossed under the apparent RFD notch, I got a noticeable blast of wind from the NW, and noticed several small trees broken off. I continued on, and as I approached the bridge over Cahokia, I began to see hail piled along the side of the road. I got out and looked at a pile, saw hailstones up to 1/2 inch in diameter. This was probably 10-15 minutes after the storm passed there, so they may have been larger when they fell. I also thought from watching the storm and from the reports I heard that larger hail fell farther north. (Note: STL LSR reports 3/4 inch hail in Carlinville at 5:41 and 1 inch hail at 5:50.)

By the time I got to the bridge, the whole road was covered with ice, roofs were white, and the piles and drifts along the side of the road were 4-5 inches deep - and there was lots of hail fog in a short stretch just east of the bridge. I would say the area where the road was ice-covered and where there was hail fog was no more than a few hundred feet, but a lot of hail had fallen in that narrow path. Had I not been slowed from my previous stop, I could easily have skidded on the icy road. I turned right when I got to route 4 and went through Staunton. The streets were almost totally flooded in places there, but there was no hail on the ground. From there I continued home to Edwardsville via 4 and I-55, as the storm went outflow dominant and gradually died to my east, and another one cranked up to the SW, prompting severe T-storm warnings in St. Louis City and County and St. Charles Co., MO. Nickle-size hail was reported with these storms, as well as a 55 mph gust near Lambert Field. (I think this storm may have taken some of the energy from the one I was on.)

Obviously, the cold air aloft was a factor in the prolific hail these storms produced. But they were strong storms in their own right - the one I was on really had the look of a supercell, and the persistence as well. It moved slowly south from just west of Lincoln to just east of Staunton over a period from about 2:30 to about 7:00 p.m. There was some storm-relative shear, as the surface wind ahead of the storm was from the SW, the storm moved S or SSE, and the anvil drifted off to the ESE. A pretty interesting storm for a day when nothing was "supposed" to happen.

Photos and video stills of this storm can be found on my Weather Photos Page.

Total chase distance: about 55 miles.

John Farley jfarley@siue.edu