PORTIONS OF NORRIS GEYSER BASIN TO REOPEN TO PUBLIC
Note that this press release refers to the "annual disturbance" that I referred to in earlier replies (see above). I thought that it normally occurred in autumn, but the press release indicates that last year's disturbance was "larger and longer than normal", which could also indicated it started earlier than usual.
One thing about the "annual disturbance" -- it sometimes causes Steamboat Geyser to erupt. Here's more on the 2003 disturbance, including the Steamboat eruptions:
I wish I could go to Yellowstone every year!