STORM TRACK: November 30, 1986 (Volume 10 Issue 1)
You're out on the road day after day, driving hundreds of miles for that one chance of a lifetime. Tired and fatigued, you wonder who will pass out first, you or your chase car. Sun baked and dry, you both press onward across the plains. But, hey, its your lucky day. A slow moving supercell pops up in front of you. Crisp towers boil through the sky. All your experience and expertise is there. You savor the chase, carefully maneuvering into position closing on the southwest portion of the rain free base. Suddenly, a wall cloud warps into view, and then a massive tornado forms. Excitement is suppressed as you think about the best location to set up your film equipment. You're cool. You just know this will be the best tornado footage ever. You imagine every newspaper and television station will pay top dollar for the film rights. You wouldn't even be surprised if you were invited to appear on the Johnny Carson Show. After all, you are one of the best, the Indiana Jones of storm chasing. Rounding the last hilltop, your jaw drops open, all thoughts are dashed. You're in shock, not because of the tornado, but by all the people eagerly filming "your" tornado!
Yes, video is popular these days. Just about everybody has one, or access to one. Such was the case on July 28, 1986 near Sioux City, Iowa. A slow moving supercell spawned a tornado which lasted over 20 minutes, was highly visible, and filmed by over a dozen people. The tornado moved southeastward across the Missouri River and struck an Iowa Public Service Power Plant causing about 30 million dollars in damage. I was impressed not only in the high quality of these films, but of tremendous scientific value they will have in the study of tornadogenesis.
The films clearly show the life cycle of a tornado can be extended by being "passed" to the next updraft. This tornado went from the organizing stage through the mature stage to the shrinking stage in ten minutes. As the tornado was roping out, a second wall cloud develops rapidly just to the east. The tornado now thin and contorted is pushed by the wrapping rear flank downdraft toward the new wall cloud. Over several minutes, the thin tornado enters the organizing stage widening into a massive cone-shape vortex. As it crosses the river, a shower of sparks indicates the tornado hit the Power Plant. The tornado heads southeastward in the mature stage for another 10 minutes. Finally, the tornado ropes out for good. I have never seen this cyclic behavior where one tornado is passed to two updrafts. Have any of you seen this happen? Burgess, Davies-Jones, Doswell, Moller, Snow? Any comments?
The films appeared on KTIV-TV 4 in Sioux City, IA on FOCAL POINT, a half hour program of local events. TV personality Van Carter narrated the show with National Weather Service guest John Wooldridge. A description of the best films follow:
Marvin Theobar filmed the beginning of the tornado. He was at Southern Hills Mall looking southwest. Through the rain, the outline of a wall cloud could be seen a few miles away. A funnel formed on the west end of the wall cloud then dipped toward the ground. A clock display on his camera screen showed 7:40 pm. The vortex appeared V- shaped with an occasional debris cloud. By 7:45 pm, the tornado had moved southeast away from him. At 7:48 pm, the tornado became narrow and two minutes later almost roped out about 7 miles away.
Robert Sikma was also in the rain at Riverland Estates near Ponca, Nebraska. He was looking south at the tornado from the Missouri river. The tornado was rope shaped and contorted about 10 miles away. Video was taken during the mid-life of the tornado.
David Jenkins from Dakota City, NE won the award for the most picturesque tornado. The cone shaped funnel formed just above him and touched ground on the the adjacent farmstead damaging some outbuildings. The funnel appeared a blue-white color. He was so close to it, he had to pan up and down the tornado from cloud base to ground. The video shows dust and debris being picked up in wisps. Dave got in his pickup and drove away from the tornado, one hand on the wheel, the other on the video camera. A few miles away, he felt safer, and stopped to film the tornado as it went into the rope stage, crossed the river, and hit the power plant in a shower of sparks.
Looking east, you can see the tornado begin to intensify again as it approaches the new wall cloud. Trees in the foreground bent southeastward in strong downdraft winds.
The storm chaser of the year award goes to Mike McKennah. Mike should be glad he is alive today as he was very close to the outer fringe of the tornadic circulation. Only half the base of the tornado is visible on portions of his video. The base of the tornado appears like a dish with rapid low-level inflow on all sides with outflow at about tree level. It is dark as night, and the vertical motion of the dust and debris is as awesome as the Brooklyn Center tornado filmed earlier this year.
Jay Severson was southeast of the storm and took excellent video of the updraft structure to anvil level. The updraft appeared as a vertical cylinder with helical cloud striations. The base of the updraft was like a dish, lowest in the center with a large V-shaped tornado. A truly isolated supercell storm.
Other notable film stars were Loren Jorgensen of Sergeant, IA, Hal Dalhower of Homer, NE, Dave Smeddar and Jim Jacob from Ponca, NE plus three anonymous videos. As the television show ended, Van Carter's last comment was "The next time the tornado strikes, get out your camera!"
