[jeramey]

VHF (FM radio in the US is in the VHF band) propagation can definitely change at different times of day.

One of my favorite activities in the summer is to go get lost in the Cascades, and when the sun goes down, settle in to a hammock with a little multi-band radio to see what I can pick up. As the evening wears on, I can typically start to receive FM radio stations in Canada several hundred kilometers away. Once the sun has risen again, I can no longer tune those stations no matter how much I fiddle with antenna orientation. NOAA weather bands also become easier to tune clearly at night.

As to why VHF frequencies seem to propagate better at night, I could only speculate, but they do seem to—at least on occasion.

[askvictor]

From https://en.wikipedia.org/wiki/Skywave : > Because the lower-altitude layers (the E-layer in particular) of the ionosphere largely disappear at night, the refractive layer of the ionosphere is much higher above the surface of the Earth at night. This leads to an increase in the "skip" or "hop" distance of the skywave at night.

Also came across this interesting page: https://www.fcc.gov/media/radio/am-stations-at-night

[jeramey]

Oh cool, I hadn't heard of E-skip as a phenomenon before! Thanks for that info, it's really interesting.