As of mid-August, they're alive and well in Mt. Rainier NP. The above photo was taken by Rick Wong just above Edith Creek on the Skyline trail,about the 5,600 foot elevation. So the wildflowers are still in bloom in some meadows in the NP this late in August. You can get more information about wildflowers and a map of meadows.
Another hiker has her photos from a hike over the weekend of the wildflowers and Mt. Rainier on the same Skyline trail. So, the opportunities are there.