Summer in the Rocky Mountains is highly volatile. We will be hiking mostly between 8,000 and 12,500 feet with temperature swings from possible highs in the 80's to lows in the 30's. Passes will likely be windy and the mountains are well known for afternoon thunderstorms. It probably won't snow, but it could. The bottom line is to BE PREPARED FOR EVERYTHING.
The layers that you bring should be on par with the diversity in the weather. You will want to have easy access to a warm layer and a rain layer (such as a poncho).
If you have any questions about your choices in gear and/or clothing, feel free to post them here for all to see. Thanks.