Thanks for your input, jrgagne99. Is a "Digital cliff" referring to where the TV signal just drops off?
I have been recording signal strengths for the 7's, 10's, 15's and 38's channels today. They have all been in the 30-40% strength range, which is just fine for a good picture. The 7 channels are a bit lower but WDBJ has a known transmitter power issue.
We last had rain about 3 days ago and each of those days lousy reception on all stations except the 38's. Maybe the balun has dried out?
I'll keep recording signal strengths. If my readings are still good tomorrow, I'll take a trip up to the roof and look more closely at the baluns water-tightness.