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Weather 2000 provides site-specific statistical forecasts for Degree Days, Temperature, Rainfall, Snowfall and more. Since the Weather Risk Market's origins in early 1997, Weather 2000 has conducted hundreds customized long range forecasts. Contact us today to see how a long range forecast can help your business.

Understanding Degree Days

Degree Days are the most common and popular weather variable utilized for energy trading, weather risk management and seasonal planning, used to determine cumulative temperatures over the course of a season. Originally designed to evaluate energy demand and consumption, degree days are based on how far the average temperature departs from a human comfort level of 65 °F.

Simply put, each degree of temperature above 65 °F is counted as one cooling degree day, and each degree of temperature below 65°F is counted as one heating degree day. For example, a day with an average temperature of 80 °F will have 15 cooling degree days. In very warm or cold locations, an alternative base such as 55 °F or 75 °F may be used.

Degree Day accumulations are proportional to the amount of heating/cooling needed for a building to reach the human comfort level of 65 °F. The degree days are accumulated each day over the course of a heating/cooling season, and can be compared to a long term (multi-year) average, or normal, to see if that season was warmer or cooler than usual. The graphic below shows normal heating degree day accumulations over the full heating season (Source: NESDIS, NOAA).

Degree Day

(T - 65)
Daily CDD
T is daily Average Temperature (°F)
If T is less than 65°F, CDD=0
Degree Day

(65 - T)
Daily HDD
T is daily Average Temperature (°F)
If T is greater than 65°F, HDD=0
Average Temperature of the day Tmax + Tmin
Tmax (High) & Tmin (Low) are whole integer values

NWS vs. Financial Industry Methodology

Degree Days are officially observed by the National Weather Service (NWS) and officially archived by the National Climatic Data Center (NCDC). Since the NWS rounds average (mean) daily temperatures to the nearest whole number, official degree day records contain only integer totals.

The Energy and Financial Industries typically prefer not to round daily average temperatures for their contracts, thus fractional degree day values are documented (0.0, 0.5)