I have the exact same problem here in Illinois! It hits mostly between channel 150 and the upper 200s but definitely the Discovery channels and especially TBS and FX. It also takes out the HD feed of our local ABC channel (187). Starts around 5:50p and keeps it up until about 11p. The rest of the day, the channels are fine.
It's been happening for about a month and seems to be getting worse. At least now I know I'm not going nuts.