Have you tried moving the antenna up or down, or side to side? I'd guess you are in a local null for RC 35, which goes away when the atmospheric conditions are right (ie at night). Look here
http://www.hdtvprimer.com/antennas/siting.html for some insight about nulls.
The TVFR is just a simulation, and does not have the spatial resolution to pick up local nulls on the scale of the wavelength, if that's what you are experiencing.
BTW there is an entire hobby called DXing (distance listening) that aims to pull in distant radio and TV. Hard to say why you received KNTV ...