Not a lot of warning. The news that morning mentioned rain for the evening. When we got home from work, we cooked dinner and then sat down to a nice movie.
It's hard to notice the clouds moving in when 6 speakers full of gunshots are going off around your head

First warning that the rain was more than just a shower was a large lightening strike followed shortly by the tv clicking on and off.
I know a power conditioner won't stop the tv from shutting off in this case, but I'm hoping the large transients will pop the breaker on the H15.