With the weather advantage, all of the eclipse experts have all the sophisticated weather resources you would want, there are special weather products coming just for the eclipse from various people including a met here in Canada. The average viewer may not use or know about the various sites that will start operational forecasts, but all the experts will. I have to keep reminding myself its not just weather systems and pulses, its plain clouds that might form which is far more insane to pinpoint to the exact spots within 1 minute intervals.
Even if your very close to the path of totality (in IN), there is no chance you will make it if you have an appointment at 10 am (even a 30 min drive). The traffic gridlock will be beyond anything you can envision. I think it'll be the worst in southern IL and MO but in places like OR the emergency management for that state who aren't blowing hot air, state if you live 2 hours outside the 70 mile path - leave SATURDAY evening to get there at 11 am MONDAY on the west coast. So a 2 hour drive would take 32-36 hours!!! No one really knows what's going to happen but once there was a 3 day traffic jam in China so its not impossible to get this kind of traffic.
I woke up one day with that question and read that if its a dense overcast during totality it will be so dark you won't know your way around. Can't say if that's true for certain.