===== 19 Apr 96 Central IL Tornadic Supercell ===== by Roger Edwards NOTE: Because I keep detailed logs, my written chase accounts tend to get very long. If you have no interest in a blow-by-blow of the early tornadic stages of the Springfield/Decatur/Urbana storm, stop here. CHASE FORECAST: Rich Thompson and I had been anticipating supercell potential in west- Central IL for several days, helped by a very consistent ETA model which had trended in all the "right" directions from run to run. In particular, with instability not expected to be a problem, ETA storm-relative wind forecasts at low, middle, and upper levels for the evening of 19 Apr stayed within tornadic supercell guidelines (Thompson 1996, SLSC paper) over the eventual target area. Also, the "nose" of the low and mid level dry intrusions was aiming the same way. All the favorable parameters were so well overlaid in the forecast atmosphere over west-central to central IL that each new model run was a virtual neon sign flashing, "TORNADOES HERE." The only negative factor was the fact that I could take the day off; which had always been the most reliable chase-bust predictor before! I'd seen too many "near-certain" outbreak situations go awry to get too excited; but we planned strategy well in advance just in case. We decided the evening before to leave Kansas City late the next morning, drive to the area between Quincy and Springfield, and get 40-60 miles ahead of expected eastern MO convective initiation. This "bullfighter" strategy would allow us to 1) get good visuals from the relatively open country in that part of IL, 2) pick a target storm from east of the Mississippi, and avoid dealing the river at crunch time, 3) get far enough ahead of the fast-moving (35-40 kt) storms so that they would have time to organize into tornadic phases by the time they reached us. The late evening (19/00Z) and chase morning (19/12Z) model runs kept flashing the same sign even brighter. The whole situation was so well-defined it was almost scary. "Something HAS to go wrong today; Rich and I are both off and can chase in an outbreak scenario!" [I should have looked harder at the maps; towns in that area include Prentice, Burgess, Curran, and Kellerville!] THE CHASE (Open your road atlas to IL): After a leisurely 7-hour drive from Kansas City in the MEATWAGON, we parked at 1615 CDT just east of Pittsfield IL (W of Springfield). After 5-10 minutes, we saw anvils erupting to our NW, WSW, and distant S. The one to the WSW was closest, moving right at us, and showed explosive development judging from the anvil evolution. Although the boundary layer haze still kept the base out of view, we decided to head farther east and allow time for the storm to evolve. We heard a SVR warning for Ralls County MO -- the same storm. As we were jockeying for ideal vantage between Florence and Winchester (1710 CDT), we heard a tornado warning for this cell on the IL side. We found a great vantage on the E side of the Illinois River valley, 5 WSW Winchester. We become a red cape for the charging bull, which would almost gore us. By 1728, the rear flank rain-free base had risen off the horizon; with the S edge of the core due W and approaching fast. Anvil rain had been falling on us for nearly 30 minutes. From 1735- 1740, a rapidly rotating wall cloud formed due W and was moving our way at 40 mph; and hail to .75 inch in diameter fell. Scud S of the wall cloud began to rise fast and surge toward us: a powerful RFD was wrapping around the S side of the meso, the E edge of which by 1742 was less than a mile W. We repositioned to face S, in case we had to bail out in a hurry. At 1744, a dust whirl showed up in a field roughly 300 yards WSW, right under the interface between the RFD and the S rim of the mesocyclone, and started cruising right at us. We bolted S about 200 yards to let it cross the road behind us. While Rich filmed, I got out of the car just long enough to glance up and see the scud and cloud base spinning extremely fast: this was the real deal! The tornado quickly became enshrouded in dust and rain; and was no longer evident after 1746. We had to go S, E, then NE to catch up; the N option was cut off. In the meantime, we got caught in a heavy and very annoying shower near Glasgow that slowed us down and killed our view for a few minutes. Then, going N through Woodson toward I-72, we got stuck in a 10-car backup behind a pickup moving 25-30 mph (in a 55 zone). Sound familiar? We decided to head east on I-72 to make up time; but the supercell had a little surprise: Going up the entrance ramp at 1818, a sunlit cone tornado appeared to our NE, about 4 ENE of South Jacksonville IL. We closed in on I-72, exiting onto a local road that runs parallel to and about a mile S of the Interstate. With the tornado about 2 miles to our ENE, suction vortices briefly appeared. It appeared to cross I-72 about the same time. As we got to within 1/2 to 1/3 mile SSW of the tornado at 1824, it destroyed a small non-residential structure, sending big chunks of glittering, corrugated, gray sheet metal swirling up the base of the vortex. Afterwards, the tornado became a diffuse circulation with no condensation funnel -- but occasional bursts of debris. We finally found a stopping place S of the tornado, which was by now located about 4 WNW Alexander. The parent wall cloud had narrowed into a yellow, sunlit barrel, rotating very fast and almost indistinguishable in spatial extent from the tornadic circulation. Meanwhile, 40-45 knot dry westerlies were blasting past us in RFD. The tornado and wall cloud vanished quickly, as a new flank formed to our ENE-SE. 2 E Alexander, we saw utility poles down and wet stubble strewn across the road. At 1845, a slender cone tornado (also sunlit) appeared to our ENE and roped out within 2-3 minutes. We estimated its location at 3 N Curran. Although the parent wall cloud remained visible as we got back on I-72 between Curran and Springfield, that was our last tornado. The storm got a few more miles ahead of us as we circumnavigated Springfield. We decided not to take I-72 ENE out of Springfield since the tornadic meso could be right on the interstate. Tulsa (24 Apr 93) taught me that lesson! [Later that night, we saw an image from Decatur's Ch. 20 weathercast showing the hook echo when it was right over I-72 near Illiopolis. We made the right decision!] The only other option was IL-29 SE from Springfield, which let the storm get away but gave us magnificent views of the rock-hard supercell racing off to the ENE in the light of the setting sun. We were shooting stills of a large, dome-like overshoot followed by a backshear ring, during the time (about 1735-1745) of the Decatur tornado. The supercell later spawned the Urbana night tornado shown on TWC, followed by a killer tornado at Ogden. SUMMARY: 4 severe reports (all called into WFO ILX): 3 tornadoes and one hail. Classic, cyclic supercell. Because of the fast movement of the storm and the controlled hurry to keep up with it; video and still photo opportunities generally stunk during the "heat of battle." No tripodded stuff (no time), but we shot some video of each hose and attempted to reel off a few stills now and then. All told, a hectic but rewarding chase: the rarity where the forecast, intercept strategy, and atmosphere all cooperated fairly well. Of course, I'm extremely interested in any other observations of this storm. Chasers coming down from northern IL should have had a great approach opportunity on this beast. ---------- *** No disclaimer necessary; employer not named at their request *** "Just the angular momentum has ===== Roger Edwards ===== to @$#%& do it! Come on!!!" ( ) Forecaster - former NSSL chase partner former NHC Forecaster :::::::::: http://www.nssl.uoknor.edu/~edwards/ :::::::::: "I FEAST ON THE SMORGASBORD OF ATMOSPHERIC VIOLENCE."