Always wondered. Perhaps Spirit Wolves and Doomhammer in Thrall's WC3 incarnation hinted at this but the HoTS guys are running with it. There was some doubt in my mind because of chain lightning and his ranged attack in the RTS. It's nice to be sure now, that the biggest and best Shaman of them all chose the right spec.
Tried to link it but someone will have to do it for me. You'll note however two abilities listed on the, as of yet unseen, Thrall in his Heroes of the Storm incarnation. You'll find it on the curse site dedicated to the game, linked in the most recent Mmo champ posting.
Lava Lash and Unleash Elements