Banff experiences a variety of climatic conditions. It can reach 90 F/32 C during the summer and -29 F/-34 C during the winter. Winter can start as early as October and last until mid-April, with the coldest months being December-February. During the winter, it's important to wear a warm, windproof winter coat, mitts and gloves, insulated boots and hats that cover your ears to avoid frostbite.
Those interested in warm-weather sports will find midsummer to early fall the best time to visit. July and August can be hot and dry, but be prepared for cool temperatures the rest of the year—and be aware that it can snow in the Rockies any month of the year.
Winter-sports lovers will find dry, cold weather and plenty of snow (54 in/137 cm). January temperatures generally range 3-30 F/-16 to -1 C, though the warm Chinook winds in southern Alberta can raise them rather suddenly. The mountain regions and the northern part of the province can be cold year-round. It can snow in the Rockies in any month.
Alberta boasts the title of Canada's sunniest province, with more clear days than anywhere else in Canada, making the scenic views IMAX-spectacular. June is probably the wettest month—although even then it's nothing like the steady mist of, say, the Pacific Northwest.
Mountain weather can be very changeable and unpredictable. Wear layers of clothing, which can be added or taken off as conditions warrant. If you are driving in winter, snow tires are a must.