Regarding Multipath -
For the last week or so my max signal strength has changed. Instead of having a high of about 92-93% and sometimes a dip to about 77-79%, the max is now about 84% with the same dip to about 77%.
If the 77% was due to multipath & I presume one signal canceling out the other, could the 93% have been from two signals in phase and therefore adding to other?
The new snow on your roof is probably the cause of the reduced signal. Trees leafing out in Spring and higher winds can also cause this. WBBM-12 OTA signal strength at their present power of 8 kW is a popular topic at AVS Forum. It's unfortunate that WBBM's OTA signal is left in the dust by the IND/Religous/Spanish UHF stations. I'm 58 miles out West from Willis and my custom Yagi-12 antenna w/ pre-amp still struggles to get a stable signal.