Thanks everyone for the great suggestions. I was really at a loss as to how to approach this. A colleague and I are getting guided on a one day trip on October 14th. Unfortunately, the rest of the time is booked with business. It appears that on the 14th a cold front with some rain is moving in so the temps are forecast lower than usual. The guide has suggested we decide on the location later this week. On his short list (provided a month or so ago) was South Boulder Creek, Farmers Union on the Platte, or the Bartles Lakes fly fishing club.

From the posted comments, it sounds like I should pickup a thin merino wool long underwear pant and a fleece pant as well. This way I could make a call as to what I should wear that morning when I know where I?m going and what the more precise temps are going to be. If I wear long underwear I?ll wear my nylon pants. If I wear the fleece I assume most would just wear these as pants to and from the stream? Those Cabela?s waderwise pants look nice!

A bit of web searching indicates the stream water temps are going to be in the 50?s. So my plan is if the high ambient temps are in the 30?s-40's I?ll wear the fleece pant plus the thin merino base layer. If the high temps are in the 40?s-50's I?ll wear my heavier Patagonia capilene (3 weight) base layer with nylon pants. And if the high temps are in the 50?s to 60?s I?ll just wear the merino base layer and the nylon pant. Do you think I?m on track?