Well we know from the season beginning that Walter is alone on his next birthday (he has to arrange his bacon himself) and he bought a bunch of guns, and then got the ricin in a house that was ransacked and had ‘hisenburg’ painted on the wall.
Everything has to lead up to that
So Skyler and the kids are gone.
The house is fenced off, but Walt is not in jail... and planning something bad
The bedroom door kicked in (means what?)
I dont remember what the signs on the house say (not police or FBI signs, were they? more like HazMat?)