Fishing season opens today. The Firehole will provide the best fishing with BWOs making resident fish active. Use life cycle patterns beginning with nymphs early (unless there are a good amount of rise forms) and changing over to emerger and dun patterns as the day advances. Although the Madison is running a bit high, BWOs are doing the same in the river along the West Entrance Road, so use same strategy as on the Firehole. Also for both rivers be sure to have a few streamer patterns in that fly box.
Look for all other streams in the park to be running high for some time. This is because of last winter’s copious snowfall beginning to run off.
Another thought: the park weather is likely cold and stormy, so bring appropriate gear.