Alsatian,

I never got above 10,000' on this trip. The Ten Mile and Sawatch ranges had no snow however, including the 14,000' peaks there. I will say that the San Juans hold snow longer and get snow sooner than any of the ranges in Colorado. I did an extended trip to Chicago Basin (In between Silverton and Durango) in July, and ran in to snow at about 12'000. Like you said, the weather can change in an instant. I think your chances of running into snow Oct 20 at 11,500' are above average. Good luck!