What can I do to improve TV signal?

I’ve got a decent Winegard rooftop antenna, about 28 feet off the ground, pointed toward a distant city, and unfortunately, a forest.

I’m trying to catch several signals in the 50–70 mile range, but just can’t seem to with any consistency. The one I do get only works in the morning and night, and never during medium bad weather. I’ve adjusted the direction, and bought a cheapish signal amplifier, but nothing gets better. Even nearby channels work poorly at times.

Is the forest just blocking too much signal? Could a strong nearby FM broadcast be interfering? What’s with that channel that only works from 8pm-8am? What should I try next?