So fundamentally after the crash boeing encountered recently their stock dropped 9%, which could be a spark for everyone to start shorting it. This would mean it would be difficult for the Dow to rally since Boeing holds the most weight of any other in the index.
From an Elliot wave perspective the entire impulse up may be complete and this could drop up to 50% very soon. It can continue to extend itself but very soon it will have a significant correction as the dow did in 2008.