We may think of AM radio as subject to atmospheric conditions that allow distant signals to come in sometimes but not others, such as nighttime skywave. But FM radio is also subject to this, too.
I remember when Howard Stern was on evenings on WBCN 104.1 Boston. His syndicated morning show was recorded by WBCN for airing from 7pm to around 11pm. My family owned a cottage on a lake in New Hampshire, about 100 miles north of Boston. At that distance, and with not much elevation, Boston FM signals did NOT come in during the day. But they'd come in sometimes in the evening. Luckily WBCN was one of the better Boston signals, with no local NH FM stations near that 104.1 frequency. So most evenings, with my radio and antenna positioned just right, I could listen to Stern.
It was a lot like AM skywave, although at shorter distances. WBCN started coming in around Stern's 7 o'clock start. But WBCN and a few other Boston FMs would be gone an hour or two after sunrise. Some mornings, for whatever reason, they'd still be around till 8 or 9 a.m. Some overnights and early mornings, it might be harder to pull in WBCN.
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