alioth wrote:
The medium does affect electromagnetic waves and significantly. The earth’s atmosphere is almost opaque to some RF frequencies for instance.
I am wrong on that, I am referring to RT wavelength segments 
You may get pronounced impact from air+water medium on high frequencies in GHZ bands (liquid water resonates to radar) and in THZ bands (vapour water resonates to light) but within a line-of-sight you will have very small effect on VHF/UHF from weather (e.g. snow, night duct, storms, sun) tough VHF/UHF may or may not reach space or a point on earth due to atmospheric conditions outside a line-of-sight
We rarely account for weather effects on RT while planning but we know we will have zero viability in fog as water resonates to light 
I doubt what happens in ionosphere by day/night can be called “weather” but temperature inversions at 5000ft are probably more relevant
