Answer:
The answer is A.
Explanation:
Lets prove the other ones wrong.
B) It is not based on a day to day prediction, rather days with simmilar conditions before the storm.
C) The United states is too broad an area.
D) It is not based on the ammount of days it snows per month, because on say December 15 it could be 60 degrees and on December 25 it could be 2 degrees. Also you could not make any predictions on a per-day basis then.
So the only clear answer is "Historically, in this area, it has snowed 10% of the time on days with similar meteorological conditions as today."