If you zoom out on the Wx page of your 396, I believe you will see the coverage. It does not go that far out. Years ago I was flying to one of the out Islands and could see numerous lightning
strikes on my 396, but no associated Radar
echos. I assumed some kind of glitch and ended penetrating a line of level 5 thunderstorms, so at least back then lightning
went out further than Radar
. If you get outside of the coverage, it will give you a message of XM service lost
, but you can still have coverage, but not see what is ahead of you as that is out of the area, that is what happened to me.
For sailing, I do not think it's worth the monthly cost, but if you stay in close, maybe it is.