Now it's getting really cold, and it might even snow in lower regions! Even the biggest outdoor enthusiast loses interest in "open-air business" in such weather. Please remember that your cat may struggle with frost and snow now, as the icy ground doesn't allow them to bury their waste as desired.
In these temperatures, outdoor cats that usually take care of their business outside will desperately search for a spot inside the house where they can do their business undisturbed. So, provide outdoor cats, at least in winter, but preferably year-round, with a suitable litter box indoors.