I had the same problem when moving to the Northwest, although somewhat tempered by a number of years in the east. Summer in the Rockies is about like the Cascades in spring and fall.

As I mentioned, the climate in the Rockies may have warmed up a trifle, but in my trips back I haven't noticed any change at all in the extremes I've encountered! You can still expect snow and well-below-freezing temperatures any month of the summer. I'd rather carry an extra insulation layer so I'm comfortable when that happens.

What I did notice on more recent trips back is a definite change in the summer weather patterns in the Rockies. Back in the 1940s and 50s the frequency of thunderstorms dropped way down in early August--you could expect a week or two of beautiful weather, a couple days of thunderstorms and then another clear week. Now daily thunderstorms can be expected throughout August and (per the data in your book) into mid-September. I did have a gorgeous week in the Winds in mid-August of 2008, though--it drizzled, blew and snowed high up the day I went in, but cleared that night with absolutely perfect weather the rest of the time.

I've seen too many times when the weather forecast was wildly off (technically, it changed after I was already out on the trail ) that I just plain don't trust the things! That's especially true out here when nobody, even the best meteorologist with his computer, can predict just what storm systems are going to do or how fast they're going to move over several thousand miles of ocean. I'd just as soon be prepared.