Climate Normals

What are climate normals?

Climate normals are 30-year averages of weather observations, recomputed each decade by NOAA. They answer "what's typical?" rather than "what happened this year?" The current official window covers 1991–2020.

How SnowDates uses them

SnowDates computes its statistics over the 1990–91 through 2019–20 snow seasons — the seasonal equivalent of the 1991–2020 calendar window. For snowfall dates we use medians rather than means, because a single freak September or May storm can badly skew a mean date.

Any single winter can differ wildly from the normals — that's expected. The "early/late" chips on city pages show exactly that: how the latest season compared with its 30-year normal.