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.

I have no problems camping in the rockies in September

Here is a great article on September weather in Banff. The answer is "it depends". The average daytime temperature in September for Banff is 61F (16.1C). The night-time lows average 37F (2.8C). Of course, those are averages, and you can go from one extreme to another pretty quickly. If it were me, I'd go, but be prepared to adjust your schedule in case you have to wait out a day or two of snow.

Banff Weather for September

Jim

How far north are you planning to go? When we were in Fort St John, Fort Nelson Toad River, Muncho Lake, etc.--July 2009 the temp was around 65. People in Toad River told me the average winter temp was very definitely in the minus column. As in northern Alaska you can definitely notice a drop in temp starting in Aug. Lars