The good thing is the eclipse itself has a tendency to destroy clouds -- or at least low level cumulus clouds that are fed by convection. So the probability is actually a bit better than the statistics suggest, especially in the east. Now if there are already thunderstorms developed then they probably won't die out in time, and it won't do anything for a frontal system. But at least with frontal systems you have several days of notice to move out of the way if you can.
Along the west coast the concern would be morning fog, which might not burn off in time, especially with the Sun going away. In the midwest a concern is smoke from forest fires, since it's peak of summer drought and fire season. There's a risk no matter where you are, so just gotta plan and hope for the best. And it'll be awesome no matter what happens.
I really look forward to all the comments and recordings afterward. This will likely be the most photographed and filmed eclipse ever!