Cold weather operations
After ignition, give your engine enough time to warm up before performing the engine run-up. Check your POH; usually, it is around 75-90°F.
This is much longer than in summer; there must be humidity as well as cold temperatures to create a risk of icing. So it’s not a problem when the sky is blue, but if there is fog, clouds, precipitation, etc., those negative temperatures are bad for small aviation. Even with a basic de/anti-icing system, you may not always fly in known icing conditions and the amount of exposure time is also limited.