The numbers are all seasonally adjusted, unless you think the winters are that much worse than usual.
While I agree, the past few winters have been really bad—parts of the Northeast this past winter got essentially two winter seasons’ worth of snowfall in the space of a month. Indeed, those old enough remember the 1979 Chicago Blizzard (January 13-14, 1979), a blizzard combined with two subsequent months of below-freezing temperatures (It didn’t get above freezing in any significant way until late March!) that just about stopped all economic activity in that city and probably contributed hugely to the national economic malaise at that time.