So I turned to the film SLR, at which point the thunderstorm died down and left me with several exposures of nothingness. There *might* be one on there if my reflexes were fast enough... but I won't know until I develop the film (which is half the fun of using film).
The storm's still rumbling on nearly an hour after it started, but at a low enough rate that I'll just waste the film if I keep going with the 30-second exposure approach.