Climate Data
Climate Normal Explained: Why Forecasts Compare Weather to 30-Year Averages
What climate normals are, why they use 30-year periods, and how they help compare today weather with typical conditions.
Quick answer: A climate normal is a long-term average used to compare current weather with what is typical for a location and time of year.
Why 30 years
Thirty-year periods smooth out short-term swings while still representing a recent climate baseline.
Normals are updated periodically.
What they include
Normals can include temperature, precipitation, snowfall, heating and cooling degree days, and other statistics.
They vary by station and data quality.
How to use them
Normals help explain whether today is warmer, colder, wetter, or drier than typical.
They are not a limit on what weather can do.