Those are the % of distance flown each month.
I fly mostly for holidays so I reckon those numbers make sense. December and January are Christmas and New Years' holidays. March is (depending on the year) Easter in Europe and the start of Spring, so travelling feels good after the long winter.
I am a bit surprised April, May, June and July rank so low, but on the other hand is the weather at home is more pleasant, so less need to travel.
Does anyone keep their own numbers?