Cold-weather driving conditions vary more than you'd expect.
Some countries legally require winter tires or snow chains during certain months, regardless of forecasted conditions, and rental companies in those regions typically handle this automatically. Others leave it up to the driver to request winter equipment, so it's worth asking directly when booking.
Daylight hours shrink dramatically in northern latitudes during winter, which affects both driving time and route planning. Check road conditions the morning of a mountain or rural drive rather than relying on a forecast from the day before.