The seasonal weather throughout the Canadian Rockies and around Banff is extremely variable due to high elevation and rugged topography.
Winter (Nov - March)
Spring (April - June)
Although it can and does snow at any time of the year, the first snow generally begins to fall in November. The average temperature during the winter months is around -12º C (6º F); however it is not unusual to have a two-week cold snap during December or January where temperatures plummet into the -30º C/F range. Fortunately Banff and areas west and south regularly receive a welcome weather phenomenon called a Chinook, where warm winds produce spring-like temperatures in a matter of hours, which can last for days or even weeks.
Rain and warming temperatures begin to melt winter away from the valleys in April; however snow does not leave the mountain passes until mid-summer. June is Banff's rainiest month: this combined with snowmelt pushes the rivers to their crest.
Summer (July - August)
The summer season usually has low humidity, warm temperatures and daylight hours lasting until 11:00 p.m. at the height of the summer equinox. Average highs are about 21º C (70º F) with lows around 7º C (45º F).
Fall (Sept - Oct)
Fall sees diminishing daylight hours and warm days with cooling evening winds. Average temperatures are dropping, but highs remain well above freezing and lows hover right around freezing.
[Source: Town of Banff]