Sure, it's too early to be thinking of snow. But some things just nag at you when summer fades and the night air whispers of autumn. For example, why have five of the 10 deepest snows on record in Baltimore fallen between Feb. 11 and Feb. 19? How come seven of our 20 snowiest winters since 1883 struck since 1983? And why have 30-year average seasonal snow totals for the city slipped from 23 inches to just 18.2 inches since the 1970s?