Hip waders are good enough for small streams and creeks, even large freestoners like the Snake River where deep wading can get treacherous. Chest waders are preferred on rivers like the Henry's Fork near Last Chance, the Yellowstone River and other slow, large rivers where deep wading is useful. They are also the wader of choice for inclement weather. In short, be prepared for anything. Never assume conditions won't change.
Beautiful mornings can lead to blustery, rain swept afternoons.
The summer of 2000 saw many days in the 90's. You just never know when it comes to mountain weather. Shorts and T-shirts are fine in good weather, but inclement weather requires more preparation. For the really nasty stuff we like to start with a layer of WaderWick by Simms or Capilene or Polartech Regulator from Patagonia. All do a superb job of wicking moisture from the skin keeping you warm and dry.