Taking into account the local weather in Big Arm is an important factor for planning your visit, especially if you plan to spend your trip poolside. The hottest months are usually July and August with an average temp of 63°F, while the coldest months are February and January with an average of 26°F. The snowiest months in Big Arm are January, December, February, and March, with each month seeing an average of 10 inches of snowfall.