I got rained, sleeted and snowed on descending an 8,000' mountain pass in MT two years ago. Some 26 miles of wet, cold downhill. A few days later I descended a 7,300' pass in a pouring, very cold rain. Again, that was in June. In each case there was no shelter from the storm.
I had the exact same experience on June 22, 2009 in Montana with an ACA tour. Many were caught out in a blizzard of wet snow in Lost Trail Pass, including a certain ACA leader and his daughter who had very inadequate gear for this surprising place at this time. It had been sunny and nice on the way up the pass. One woman became hypothermic and had to be driven down to a motel in the closest town for warmth. I would never go on a multi-day tour w/o rain gear, including shoe covers and good gloves. As others have said, the rain coat serves as a good windbreaker, even when there's no rain.