outside temperature & putting air in tires

No, you should try to keep the tire up to the correct operating pressure no matter the temperature or time of year. Just add the air. Tires lose pressure over time and it seems it happens a little faster when it's winter. It is not problematic to add air, especially if the tire needs it. Running with low air pressure can cause damage to the tire and if low enough, make the vehicle unstable at speed which could possibly cause a roll over.

Air compresses when temperatures get colder and expands when temperatures get warmer. This explains why the sensors may record low tire pressure in the winter. This also is the reason you should check and adjust your tire pressures after the car has set for a few hours. When you drive your car the road friction creates heat and warms the air inside the tire. This expands the air and typically raises the tires pressure up to 5 psi higher. So you may need to add a little air in the winter because of the change in the outdoor temperature. You should always maintain the proper tire pressure in your car regardless of the temperature and only adjust when tires haven't been rolling for awhile.