Fishing really well, in some areas, not so great in others. The entire west side is pretty warm; it's probably better to leave the Madison, Firehold, and Gibbon rivers alone for now.
However, everything in the Northern part of the Park should be doing really well! Definitely consider taking a trip to Slough Creek, Soda Butte Creek, or the Lamar River. The Gardner River could be a good option too.
Flies: small terrestrials (ants, beetles, small hoppers), caddis, stimulators, flashy nymphs