Hi Irving, Green Flashes are really cool. Here is a tally of my sightings.
Number of times I have purposely tried to look for Green Flash: est >100
Number of times I have sorta kinda (meaning probably not) seen one: ~5-6
Number of times I have actually, really, really, pretty sure seen one: 2
Number of times I have photographed one: 0 (I have lots of pictures of "empty" sunsets
)
Both times I have seen them have been on the ocean horizon. One on Santa Barbara coast and another in Baja. The problem for me is you are looking at the setting sun and which is still pretty bright and when the time comes you can sort of convince yourself that you saw another color which I think can be confused with an afterimage.
Despite my low success rate I don't think they are all that rare really. I think it happens more often than one might think it's just people aren't looking for it or notice it for what it is. Good idea to use a webcam - though it might be a little hard with the wide field of view. That offshore marine layer probably won't help with the chances but on clear days certainly worth a shot.
Now that I live in the high desert I won't get as many opportunities (no ocean). But one over land would be pretty cool so I'll keep trying when the situation presents.
-carl