When using Furios Charge - merciless assult with Sprint - run like the wind the hits from tornadoes will count as hits for the furios charge. So you could basically endlessly charge on even 1 mob ( bosses too ) if you have a tornado on it.
Edit:
This works with all rune effects so if for example you use the dreadnought rune to gain life you will gain life when the tornadoes tick - so you can gain more than 1 tick on 1 mob from a single dreadnought use.
Thanks Falreigimer for the tip.
Basically Blizzard did poor work with furious charge - you gain a buff when you start it and when the charge ends you lose the buff - what this means is that during the charge all your tornadoes will be buffed aswell dealing more damage and activating all on hit effects.