Saturday was a dramatic weather day. I've never heard the weather teams emphasize the danger of the tornadoes quite as much as they did on Saturday evening, especially as the tornado approached Wichita. I was in the basement watching the track on TV when we lost power about 10 minutes before the tornado was supposed to hit Wichita. So I sat there in the dark, listening to the increasing intensity of the rain, hail and wind and watching furious lighting flashes through the window. The tornado passed through the city about 5 miles from our house (give or take a mile or so). Luckily it was starting to loose steam by the time it hit the city. Lots of property damage but luckily there was plenty of warning and nobody was killed.
The EXIF for your image shows that it was taken about 8:45 PM, so yes, it would have been pretty dark by that time, and as you said, the clouds were moving through pretty quickly. I think you might have been more successful if the storm had been moving slower. Lots of folks that like to take lightening images find that using a lightening trigger improves their chances of catching lightening dramatically. Hmmm, from the way things are shaping up, that might be a good investment during this year's tornado season. :-) (Looks like you can pick one up on Ebay for about $117.)
Without the trigger, you basically have to get lucky with your timing. (Take lots of shots) You could have shortened the exposure time and gained a better rendition of the storm (if you were lucky enough to get a strike) by shooting at a wider aperture and bumping up your ISO a bit. Given how far away the storm and horizon are, and the fact that you were shooting at a wide 17mm, I think f5.6 or f4 would have given you plenty of depth-of-field, and I think you could have safely shot at ISO 400 without too much noise creeping into the image. All that said, your storm images are a lot better than mine. :-) Kudos to you for getting out and photographing.