What is a degree day?
Degree days are measures of how cold or warm a location is. A degree day compares the mean (the average of the high and low) outdoor temperatures recorded for a location to a standard temperature, usually 65° Fahrenheit (F) in the United States. The more extreme the outside temperature, the higher the number of degree days. A high number of degree days generally results in higher energy use for space heating or cooling.
Heating degree days (HDDs) are a measure of how cold the temperature was on a given day or during a period of days. For example, a day with a mean temperature of 40°F has 25 HDDs. Two such cold days in a row have 50 HDDs for the two-day period.
The West North Central division had the highest number of heating degree days in 2023.
Cooling degree days (CDDs) are a measure of how hot the temperature was on a given day or during a period of days. A day with a mean temperature of 80°F has 15 CDDs. If the next day has a mean temperature of 83°F, it has 18 CDDs. The total CDDs for the two days is 33 CDDs.
The West South Central division had the highest number of cooling degree days in 2023.
What do people use degree day data for?
People study degree-day patterns to assess the climate and to assess the heating and cooling needs for different regions of the country.
What are population-weighted degree days?
Degree days can be weighted according to the population of a region to estimate energy consumption. The U.S. Energy Information Administration (EIA) uses population-weighted degree days to model and forecast energy consumption for the United States and for U.S. census divisions.
Where can people find degree-day data?
Newspapers may publish degree-day information in the weather section. Electric and natural gas utilities may publish degree-day information on their websites, and some utilities include degree-day data in customer utility bills. Several weather data-related websites publish daily high and low temperatures and degree days for specific locations. The National Weather Service Climate Prediction Center is a source for historical temperature and degree-day data for the United States.
Historical monthly (from 1973) and annual (from 1949) population-weighted degree-day data for the United States and U.S. census divisions are available in Tables 1.11 and 1.12 of the Monthly Energy Review.
Historical monthly and annual population-weighted degree days for U.S. census divisions for 20 years and a forecast for one to one-and-a-half years are available in the Short-Term Energy Outlook (STEO) Data Browser.
Last updated: October 29, 2024.