During cold weather your belt can be harder and not as soft as it should be which then can lead to a squealing belt which is normal and usually nothing to worry about.
As the cars engine and belt warms up the belt then softens again and then the squeaking goes away or should go away.
If the squeaking only happens when the belt is cold then it's just because the belt is harder when it's cold because during cold weather rubber begins to harden and as it warms up it softens again.
If the belt continues to squeal the belt could be stretched and needs replaced but if the squealing of the belt only happens when the belt is cold then it's just because the belt is hard because of the cold weather.
My trucks Serpentine belt will sometimes squeal when it's cold out and will then stop squealing when the engine compartment warms up and when the belt warms up as well.