You can also purchase the expansion pass which includes blizzard mountain and one other expansion (yet unannounced) to be released in 2017 (probably before the end of Q2).
The expansion pass provides you two expansions for a price that is slightly less than if you bought them both separately.
NOT REAL VALUES: too lazy to look those up, JUST AN EXAMPLE:
Expansion Pass: $50
Expansion 1: $30
Expansion 2: $30
Both expansions purchased cost $60. The Expansion pass saves you $10 and you get the same thing…