When Carl is Facetiming his mom before going to White Deer, he is using two different phones as the shot switches back and forth from him to mom.
The only time you see winter is in the stock footage. Every scene in the town is full of the beautiful green deciduous trees sprayed with faux snow which is impossible in December just before Christmas. Furthermore, because it was obviously shot in the late summer and was warm, cast and extras were mostly lightly clothed.
While in the bake room, Ellie lets her long hair flow free rather than wearing a cap (as the rest of the staff are), even when she's making Kringles.