My assumption has always been that it is the local latitude winter. Nothing else made sense to me. I don’t know if any renderer or other data consumer actually uses it.
My main issue with it is that in my area most of the areas that have seasonal access the access is actually based on weather that definitely varies from year to year. So for example, a routing application could not easily determine if a particular highway is closed for the winter. I am not sure what the solution to that is from a mapping point of view. Seems like you need a way in the map to point to a source of information from the authorities who actually make the decision to close and lock the gates.