I’m not sure about what is normal- but should be expected. Your furnace running the hot water through your baseboards has a max capacity that generates a maximum amount of heat in the house that you cannot change. You’re probably maxing it out this weekend like most folks

Think of that that heat coming in to your house as water flowing into a dam. The temperature in your house is like the level in the dam, equal flow in and out means the water height stays constant, and the same is true for the temps in your house.

Your house loses heat through leaks. if the leaks amount to more than the amount of heat coming in, temperature begins to fall, same as the dam analogy

For any given wind speed, the amount of heat that you leak out is proportional to the difference in temperature (outside - inside).

Bottom line- when it gets really really cold, your temperature inside will drop until the heat coming in matches the heat leaking out. You get two primary options to fix it- buy more heat capacity, or reduce heat leaks.