I don't know if it is 80%, but it's a lot, that's true. My kids' school has already said that if there aren't power issues, they just have a remote day instead of a cancelled day.
I guess...this evolution of gaining latitude to a point and then just splitting east has been the theme for a while. It's about how much latitude it gains. That run did it what, 40-50 miles south of 12z? I think that's still easily within the spread of the ensembles.
He's not wrong about a likely sharp cutoff. And he may not be wrong about where it sets up. What people think he's wrong about is his level of certainty about it.