Why, I wondered, am I seeing this nocturnal animal during the day? Here, from the Opossum Society of the United States, is the answer:
There are a number of reasons for opossum sightings during the day. If it is winter in an extremely cold area, usually covered with snow, then the opossum may be hungry. It is often difficult for an opossum to find food in extremely cold, snowy areas. During sever weather the opossum may stay in a den a few days until hunger drives it out of hiding. The opossum may have to forage for food during the day, often while it is warmer.