These aren't freight trains, these systems can literally stop and turn on a dime once they become influenced by a different feature. If you have a rapidly weakening blocking high to the north and other features in place that would draw the system due north, it wouldn't take long at all for this system to stall and begin moving quickly north. (I'm fairly certain I'm preaching to the choir here, but the statement was made) It can absolutely be in Gatlinburg in 12 hours.