In the flashbacks to 1992, Paul's birthday coincides with a massive snow storm that shuts down Manhattan. Paul's birthday in the series is April 19 and that date in 1992 was in the middle of a cold wave (for that time of year), but the temperature was in the low 40s that week and the city did not experience the sorts of blizzard shown.
As Paul stands half-asleep leaning against the neighbor's apartment door, someone opens the door and Paul falls backward inside. From the way he falls, it's obvious that someone inside the apartment catches him and quickly but carefully lowers him to the floor.