Well you have kinda the right concept but a trough or front doesnt have to be that far down to mess up to ridge or reframe the ridges shape. For example the first trough is moving quick and isnt real strong but enough to have the ridge near Franklin erode on its NW side causing a weakness and pushing him around it. Now ridges are like bubbles,,,they are in many shapes and sizes and slide around and dissapate. A 2nd stronger trough will move down off the east coast and weaken the ridge and push it into the eastern gulf with a stronger ridge then off south of Bermuda. Now even though there is no cold front inbetween the ridges over the SE US or SW Atlantic there is no ridge. So its called a weakness.
I explain things kinda hard. I guess thats why Im not a teacher but I hope it gives ya some kind of idea.