Upward lightnings happen frequently enough, there is a guy called Tom Warner that has done pretty extensive research into this including high speed photography.
I was shooting time lapse during a thunder storm and caught a ground to sky lightning bolt. I assumed that if I had an image of one that it must be a fairly common kind of thing, because I know I don't have that kind of luck. Then again, I also had a time lapse of the Milky Way that someone point out something I had caught being a meteor coming straight at camera recognizable by the ionized trail it left behind which took minutes to dissipate. It definitely helps to have a shutter open. You'll miss 100% of the shots you don't take (to borrow a sports phrase).
