The image above is the risk for severe weather 30% or above in the next 4-8 days. When you get a 30% risk, you begin to get into some hot water in the weather world. 30% basically means severe weather will happen and it could happen with strength.
Day 4 (D4), we see a risk area over the Plains into the Midwest. It is shaped in the form a bow echo storm would usually have.
That said, The Weather Centre is definitely eyeing the possibility of a bow echo storm. Should a bow echo develop, it would have potential to cause damaging winds.
The 6z GFS is even pointing at the prospect for a squall line after reviewing the Best Lifted Index images. However, there will be the Canadian air mass that will fight quite hard to keep the severe weather away from the Great Lakes and Ohio Valley. However, that air mass suddenly retreats, leaving the door open for the squall line to come through. However, it does weaken as it comes through, which many of the models have shown.
In Day 5, that squall line suddenly gets a second wind and fires up with more instability in the Ohio Valley. I am unsure of what type of storm it will be, but likely not a squall line or a bow echo. I would anticipate pop-up storms, possibly coming together to form a multi-cell storm complex.