Is Sept too late for visiting Canadian Rockies?

As a Canadian resident we stay in Canada from Mid April til Mid Oct. We stay west of Calgary in Alberta so we are not to far from the rockies in south Canada. We get snowed on once or twice before heading south in mid Oct and once or twice in late Apr. Sept could be a mixed bag but the tourists will be less (kids in school etc). You could have 70 degrees or 40, totally sunny or rainy. We like to go to Banff in Sept and its usually fine. Sept won't be like summer but it would be rare to see snow.