Currently, Blizzard Beach only has hours posted through December 25th. But take that with a grain of salt though, because they're always adding/changing hours.
The thought is that when Typhoon Lagoon does re-open, BB will go into their refurbishment. Some people have speculated that TL may re-open as early as January. Currently, TL is being refurbished now.
Disney hasn't announced anything in regard to BB going into their refurbishment, but I would imagine it will happen sometime this winter regardless of TL's status, as they'll want at least 1 water park open for the Spring/Summer.
You're right that water parks won't open if it's too cold. You never know what January weather will bring. Check the weather before you leave home and bring your bathing suits just in case.