The low temp and low humidity tolerance will vary from clone to clone. *Steve Stewart was breeding a bical that could tolerate more cold condtions. *It depends on the individual situation. *
For us, the lows aren't the problem. *We have observed bicals exposed to temps in the upper 40's F for a few hours, with no problems at all. *As long as the day time temps are in the 80's or 90's F, and humidity is constant, the bicals are happy. *
Keep your bical sheltered and try to avoid any dry and cold air movement. In combination with warm day temps and high humidity, the cold temps aren't as much of an issue.