The tailwater sections of streams fish well all year round. It is worth
bringing your gear if you can find time to spend on the river. As for
recommended flies it depends on the stream you plan to fish.
Here is what Pat Dorsey recommends as effective patterns for the Platte this
time of year: Midges and midges and...

Wow! Quite a list, all small, and I've only heard of a few of them.
I'm a bit old fashioned I suppose.
My son is wintering over in Dillon and I suggested he leave some
snowboarding junk behind and make some space in his car for a rod &
gear but he didn't. I received an "Uh Oh. I shoulda" call shortly
after he arrived and saw folks fishing the Blue. He was there well
before the snow and had plenty of time then to fish though it may be a
bit out of his league. It looks like a very nice stream and he could
learn a lot from it.
I really appreciate the list and will begin to accumulate/tie some of
the flies you suggested.
From the still excited calls I get from him it appears just this one
winter there is not about to get Colorado out of his system.

Many thanks

Kiyu