Seasons and sky
Cooling Degree Day
Direct answer
Cooling Degree Day: A Cooling Degree Day is a temperature-demand index accumulated when a day mean temperature exceeds a selected base.
Cooling Degree Days estimate warm-weather cooling demand above a base temperature.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Heating Degree Day, Frost Date, Astronomical Season, Equinox
Cooling Degree Days estimate warm-weather cooling demand above a base temperature.
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The story behind Cooling Degree Day
Energy analysts paired cooling and heating degree days as climate-sensitive planning metrics.
Why Cooling Degree Day matters
They help compare hot seasons, plan electricity capacity, and normalize air-conditioning demand.
Cooling Degree Day in practice: an example
With a 65-degree-Fahrenheit base, a daily mean of 80 contributes 15 Cooling Degree Days under the simple method.
Where readings of Cooling Degree Day go wrong
A common error is to infer heat-health risk or indoor conditions from cooling degree days alone; humidity, nighttime minima, vulnerability, and building design differ.
Sources and editorial method
Research references used for this entry include:
- NOAA NCEI: U.S. Climate Normals - Official methodology and data for climate normals, degree days, growing seasons, and freeze dates.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
Track accumulated cooling demand
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Common questions
What is a Cooling Degree Day?
A Cooling Degree Day is a temperature-demand index accumulated when a day mean temperature exceeds a selected base.
What do people get wrong about a Cooling Degree Day?
A common error is to infer heat-health risk or indoor conditions from cooling degree days alone; humidity, nighttime minima, vulnerability, and building design differ.
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