Problem(s) Encountered:

The dome azimuth stopped reading during an exposure, with the result that the dome repeatedly kept trying to correct its position because it couldn''t see that it was moving, and walked away from the target.  

Solutions:

It was still early, so I called Eric; we established that neither direction was registering. He suggested power-cycling the dome connector box near the top of the ladder in the dome.

When I went to do this, I discovered that the wastebasket that is being used temporarily to shelter the box had blown off the ledge in the high wind, taking the box with it -- the box was hanging by the threaded connector, and the other had pulled out.  

Simply re-connecting that connector solved the problem.  I closed shortly afterward due to high wind, which is a rarity in my long experience. (Thorstensen)