APRIL 28, 1991: ANOTHER CASE OF TORNADO-PRODUCING MINI-SUPERCELLS

by Jon Davies

From Storm Track

© Copyright 1992 John Davies

After a rather quiet April 1992 weather-wise in Kansas, one remembers the wild and active April of 1991. Two days after the Andover tragedy, a very interesting tornado event occurred in Pratt County.

The weather map on April 28, 1991, showed a strong dryline bulging into southwest/south central Kansas at midday, with a very cold pool of air aloft on the morning upper air maps. Southwesterly winds driving the dryline eastward converged with breezy southeasterly winds ahead of the dryline, and by early afternoon low-topped storms began developing near Dodge City near the intersection of the dryline and a cold front. Bob Johns at the National Severe Storms Forecast Center in Kansas City recognized the situation as a potentially tornadic one, and issued a tornado watch for the area.

From west of my home, I watched the towers build to the far northwest and spread out into short fuzzy anvils at what looked like only 30,000 feet or less. When the Dodge City NWS office issued a severe thunderstorm warning around 2 pm for northwest Ford County, I was tempted to head northwest with my camera to the front/dryline intersection. However, a similar synoptic situation on March 11, 1990 (see Weatherwise, October 1990 issue) had generated tornadoes with a tiny storm further southeast along the dryline bulge. In this area small updrafts and towers were now developing where the air was more unstable and a stronger dry/moist contrast existed along the dryline. I elected to stay in my local area to see what developed.

I parked on a dirt road in western Pratt County and watched several updraft towers lean sharply over to the northeast, a sign of good vertical shear. Gusting east-southeasterly winds at the ground contrasted nicely with the southwesterly flow aloft, seerning to indicate good potential for storm rotation if any storms could get going. Meanwhile, I sat on the hood of my car and took in the welcome smell and feel of a breezy spring day in Kansas. The wheat was just tall enough to flow in the wind like smooth ocean waves, a reminder of how beautiful the plains can be at this time of year.

The dryline continued its slow move to the east, and I soon had to reposition myself northeastward to stay with the short towers that were trying to become thunderstorms. Inflow winds scooted clouds of dust across dirt fields as I passed under one of the updrafts, but I encountered no rain. I took up a position several miles north of Pratt to continue viewing the stubby updrafts now 8 to 10 rniles to my west as they began growing anvils that were low and poorly-defined.

Shortly after 4:30 pm, the narrow base of the fourth cell from the south end of the line took on a striated appearance, with small inflow tails visible on both its south and northeast sides. Soon a protuberance appeared at cloud base, and a narrow funnel extended to the ground.

The tornado was on the ground for 10 to 15 minutes, passing near the town of Byers and alternating between a moderate rope and a narrow funnel in appearance. Around $100,000 damage occurred to irrigation systems and one farmstead. It moved nearly due north for nine miles into Stafford County where it dissipated shortly after crossing the county line around 5 pm.

Instead of attempting to get closer, I was content to watch the tornado from a distance of around 10 miles, fascinated by the short and narrow low-precipitation "storm" that was producing it. As with the March 11 case, I saw no lightning and heard no thunder. The Garden City radar observation after the tornado had dissipated indicated RW- and an echo top under 24,000 ft. Yet the storm had distinct rotational characteristics and a significant clear slot on its southwest flank. This was clearly a small supercell and the tornado was no landspout.

After the funnel had retreated back into the cloud, I turned my attention to the three small cells further south. The second cell from the south end of the line was approaching my location and a few sparse drops of rain spattered out of its small anvil around me. This time I did hear one crack of thunder. Soon, the narrow cloud base took on a rounded flanged appearance, and a dirt cloud began to boil up about 1-1/2 miles to my west, accompanied by a small clear slot in the cloud base to its southwest. No funnel was visible at cloud base, and the dust whirl lasted only a few minutes as it moved north and dissipated. I moved northeast to stay just ahead of the short line of cells, but saw no more tornadoes. After 6 pm, the southeast winds died off significantly, and the storms lost their individual cellular appearance while continuing to put out little or no rain.

I've lived in Pratt County for the majority of my life, yet have never seen such small storms produce tornadoes until this case and the one on March 11 of 1990, both events occurring within 25 miles of each other. Part of the allure of observing storms is the possibility that you will see and learn about something you haven't encountered before. Thinking back to March 11 and April 28, I will continue to be reminded of that.


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