Difficulty: Strenuous if you go all the way to the lookout hut, particularly in snow.
Hazards: Hard Snow and a glacier moat to deal with.
Three Fingers Lookout trail is located off the Mountain Loop Highway outside of Granite Falls. Three Fingers and White Horse are both visible from Interstate 5 as well as from Darrington. The lookout constructed in 1929 is no longer manned for fire watch and is available for overnight stay on a first come basis. Be sure to check the sign in log at the trailhead to see if anyone is ahead of with similar plans. You can camp at Goat Flats as well if the lookout is occupied. The hike in is beautiful with many alpine meadows along the way. Goat Flats is set up for camping and has great views of the area as well a toilet facility.
You will likely have to cross steep snow slopes on the route. In summer the melting snow will be very hard and some thought should be given to protecting against fall. If melted enough you may scramble down the moat beside the upper glacier along the ridge east of Tin Pan Gap.
There is a low class 5 rock climb of the highest of the Three Fingers summits (not to the lookout). Crampons are recommended for crossing the glacier enroute to the base of the that climb.