Dunno, but I hit snow around Mammoth Lakes, CA last year going to the "Street Vibrations Rally" in Reno near the end of September. Also hit more of it a 5am the next morning as well as some rain and mud avalanches around Tahoe. Some Harley riders from So. Calif. hit it, turned purple, and headed back. Luckily, I had heated gear. High desert gets damn cold at night too.
You can go to Weatherunderground.com (sp?) and search their town's archives for temps and weather for past dates and years along your route. Might give you a better idea as what to expect.