All my major network channels are 40 to 65 miles away and two edge at that. Rain, snow, fog etc haven't been an issue at all. I make a point of checking when it's pouring rain or snowing very hard. For my location, weird tropospheric conditions have far more impact on UHF TV reception, ranging from complete loss of normally reliable TV stations to reception of stations far beyond normal line of sight.
Here's a website that provides forecasts for such events.
http://www.dxinfocentre.com/tropo.html
I'm not a serious DXer by any means but I did start a log of oddball stations that show up during these tropo events.