Snow chances for Denver/ lower Idaho late September

We have been doing a last week of September camping trip to South Park Colorado for the last five years and haven’t had any snow. It’s a great time to see the fall colors and enjoy the cool evenings; our favorite spot for this trip is at 10,500’ elevation. Even if we got a little snow it would be gone in a day or two.

We also need to know why snow matters to the OP. Snow isn't necessarily a bad thing.

I don't see Idaho as a "surrounding area" for Denver. Possibly the OP means Idaho Springs, CO? Clarification needed here. :)

Lower Idaho? You mean SE Highlands, Snake river valley or Sawtooths? These are all different zones that can have very different climes that time of year. First snow in SE highlands is generally late October but the first frosts can hit anytime late September onward. Snake River valley is typically a couple weeks behind the highlands but not as a rule.

September snow in the lower elevations of Idaho is pretty rare. In southwest Idaho, our first measurable snow is generally late November to December. We did manage to have a white Christmas this year.

Historically, things were a bit different. We moved to central Idaho in 1981. Granted, that is high elevation. We had snow every month but August that year...not enough to stick in the off months, but even a skiff counted!

I lived at 8000 ft. West of Colorado Springs and usually 1 or 2 light dusting in September. I got back from vacation on 1st weekend of October in 2011 to a 1 footer. That was unusual. September is my favorite month to camp in Colorado. Cannot speak for Idaho.

We did Colorado sight seeing all thru the Rockies last late Sept/ Early October and had beautiful weather and no snow. Made it as high as 13,185 Mosquito Pass. Every year will be different though.

Used to live just South in Colorado Springs. Sept almost 0 chance of snow. But Oct., very likely and possible. In fact, it's almost an institutional thing to expect a dusting of snow by Halloween. Denver is slightly lower in elev., so less likely, but there's always that weird system that might move through early in the season. I wouldn't be too concerned.

In Denver it is a possibility but low. If it did it would more than likely be one of those here today gone tomorrow. Snow history is 1 inch for September and 4.2 inches for October
http://www.thorntonweather.com/noaa/snow.php shows snow history

Weather websites have historical data.