Summer officially ends on the 21st of September, the autumnal equinox. Here in the high country it ended two weeks ago, if you go by whether there is a nip in the air and the leaves have begun to turn yellow.
There are some nice fall photos on the other DrC's blog - http://cruztalking.blogspot.com. I expect the first snowfall and the first hard frost will happen sometime in the next three weeks.
We won't be here to see it. The DrsC are snowbirds: when the snow flies, so do we - to somewhere warmer.