I want to visit Bryce+Zion+Moab in mid-June. Is it a good time in terms of:
- availability of trails (e.g. open but not too much water in trails)
Is it a good time to visit? Only you can answer that.
Most visitors never go much farther than a few feet from the parking lot. Ask a ranger at the visitor center for recommendations on less crowded trails.
Go to less visited but equally scenic sections of the parks - Kolub Canyon in Zion, Needles section of Canyonlands or Dead Horse State Park, etc. The Fiery Furnace in Arches is only accessible on a ranger walk or with a permit. Not going to be crowded.
Check the visitor center for the schedule of ranger walks and hikes. They are free and usually excellent.
Take a jet boat tour of the Colorado River from Moab.