In April and May it starts warming up to the 40s and 50s Fahrenheit, though a coat is necessary most days, and at night it can still dip below freezing. It may rain or snow, though it melts quickly. The snow on mountain ridges will remain deep until late June. This is spring ski season.
The time to hike into the mountains and enjoy the access to ridge lines and alpine flowers is during the months of June, July and August. Banff gets lots of sun, and shorts and a long-sleeved shirt or T-shirt are fine in the 70-to-80-degree weather. An extra layer is needed at night when the temperature can fall into the 40-degree range. Average rain is only a few inches a month during the summer.
In September some days may be warm, but snow flurries have been reported then. In October and November, heavier layers of clothing are necessary. The fall days are crisp and clear, and the first frost usually occurs in October, although it can come as early as September. Temperatures can range from 30 to 65 in the fall. Prepare for a wide range of weather.
Temperatures in December, January and February commonly rise only into the single digits, but 27 degrees is average. Wind can make for even more chilling temperatures. In town snowfall averages about 4 feet during these months.
Because Banff is tucked in between the mountains in a small valley area, it is often protected from full-force weather fronts that sweep into towns with mountains on only one side. Banff still gets a lot of heavy weather, but the mountains around it often lessen the severity.