In Texas, it's a little different. It can be around for many months, usually during the late evening hours to mid morning almost daily. They are directional, as David mentions, as they can carry signals in a duct from generally one direction. Having lived in the Austin metro, I usually got stations from either San Antonio, Houston, Dallas or the Hill Country, but not necessary at the same time. Houston stations always interfered with Austin stations that were co-channel or adjacent to those stations. Just as I would get tired of hearing FMs that I had no interest in hearing every night for the second month straight, it would be over and I wouldn't hear them again. Sometimes it would be for a week, a month or six months.
FMs aren't the only thing that carries far distances. I've gotten ATSC TV in those areas, too, including some low power TV from Victoria until almost lunch time.