Can unusual tropospheric conditions cause normally reliable stations to fall off the cliff so to speak? Here's the current map for the eastern US
http://www.dxinfocentre.com/tropo.html
I'm in north central Ohio. This evening I can only get 5 of the 18 channels I normally receive. I just got a second HDTV and both sets have the same poor reception right now. It's such a big change I double checked the connections behind the TV, all looks to be OK back there.