You should expect at least 50% reduction in real-world range due to decreased battery efficiency, increased need for heating, increased vampire battery drain.
I agree that winter weather can significantly affect your energy usage, but the OP's statement is rather general and not very helpful or informative. Rather than talk about range, I find it more meaningful and helpful to talk about energy use rate (Wh/mi) and specific circumstances. In my model S, I do see occasional energy usage rates as high as ~500+ Wh/mi on a particularly cold winter day,
for a short trip. And if I make several short trips in one day, the energy use for the day can indeed be very high, because the cabin gets heated repeatedly and the battery never really warms up enough to enable useful amounts of regenerative braking.
But on longer trips, the energy usage decreases once the cabin is heated and as the battery warms up and regen kicks in.
Also, the OP's general statement makes no reference to temperature or to travel speed or other details -- obviously "winter" means different things in different areas of the country, and temperatures vary considerably from day to day, no matter where you are. It might be more meaningful to talk about the average energy consumption over a month or an entire winter (but maybe the OP hasn't had that long to build a record).
PS: The reason I do not find it very meaningful to talk about range is that I rarely if ever travel far enough in one day in the winter to challenge the battery's maximum range. What happens is that higher energy consumption rates mean that I need more charge at the end of the day. E.g., instead of charging from say 50% to 70%, instead I need to charge from 40% or 50% and maybe would charge higher, to 75% or 80% to provide a cushion for the next day. This is one of the reasons i keep my battery gauge set for percentage, not miles -- I do not want to get tangled up over how many "range miles" the car used to travel a certain physical distance. (I realize that some people may do more day-to-day travel and might need to concern themselves with range.)