Early on, we were poised for a 20 again.  12 miles done by 11:30 or so, enjoying a nice lunch by a water source, one of us looked up and alerted the other.  Same scenario as the previous day.  Deeply gray clouds were amassing in the west, the east and the south.  A huge drawstring bag of darkness was closed over that bluest sky. Drops began and we hunkered in some trees, protected by our makeshift tarp.  We waited through four hours of it, took down the tarp as the sky cleared, and walked another five miles or so.