The flash is much easier to see on the Gulf Coast of Florida than on the US Pacific coast. (There is a flash in the rising sun, too, but getting the timing right is practically impossible, you have to go for it at sunset). The atmosphere is clearer at sunset and there is less fog on the horizon on the Gulf. I saw it dozens of time while growing up in Tampa. My guess is you have about a 10% chance of seeing it on a clear day, which means if you live there, and know what to look for, it is a pretty common sight. Still, I had never heard of it until an article in Sky and Telescope in the early 60s alerted me that there was such a thing.