A dog walks across the snow.
a dog is outside
It generally only snows outside; although snow can be, and frequently is, tracked indoors, for someone or something to be described as walking across the snow (rather than across the surface underneath it) requires that the snow be in a continuous blanket thick enough to obscure the underlying surface, and someone or something tracking in this much snow would be somewhat unlikely.
exists e1 x1 x2.(n_snow(x2) & across(e1,x2) & Actor(e1,x1) & v_walk(e1) & n_dog(x1))
exists s1 x1.(Theme(s1,x1) & a_outside(s1) & n_dog(x1))