Nebraska's Degree Days

Introduction

Freezing weather during the winter or sweltering weather during the summer can increase your utility bills. You can find out how much of the rise in cost is a result of the weather by using a unit of measure called the "degree day".

Degree days are used to estimate fuel consumption and to pinpoint the nominal annual heating and cooling loads of a building. A degree day is a 1 degree Fahrenheit difference between 65 degrees Fahrenheit and the average outdoor air temperature on a given day. The more extreme the temperature, the higher the number of degree days. Degree day measurements can be used to describe the effect of outdoor temperature on the amount of energy needed for space heating or cooling. Hot days, which could require the use of energy for cooling, are measured in cooling degree days. On a day with an average temperature of 90 degrees Fahrenheit, 25 cooling degree days would be recorded. Cold days are measured in heating degree days. For a day with an average temperature of 45 degrees Fahrenheit, 20 heating degree days would be recorded. Two such cold days would result in a total of 40 heating degree days for the two–day period.

By studying degree day patterns in an area, the increases or decreases in heating or air conditioning bills can be evaluated from year to year. The Nebraska Energy Office maintains degree days and degree day normals for twelve cities around the state in addition to the state's degree days. By studying the locator map, find the city to which you are closest and use that city's degree days. Degree day information may also be published in a local newspaper, usually in the weather section. Information could be available from a local utility. Its public relations department may be able to provide the number of degree days in the last billing period and how it compares to the number of degree days in previous billing periods.

In the tables below, Nebraska's heating and cooling degree days are listed as well as degree day normals. The graphs compare over forty years of degree days to the degree day normals and the last two years of monthly degree days to monthly degree day normals for the state.

Degree Day Normals

Degree day normals are thirty–year averages over a baseline comparison period. The current thirty–year period used for degree–day normals is 1971–2000. The average number of heating and cooling degree days, or the degree day normals, for each month and a total for the year is listed in the last row of each table below.

Nebraska's heating degree day normal for a year is 6524 and cooling degree day normal for a year is 1008. In a year with normal weather, Nebraskans will heat their homes and businesses 6525 degree days and cool their homes and businesses 1008 degree days. In comparison, Hawaii (a hot weather state) has 20 heating degree days and 3002 cooling degree days, and Colorado (a cold weather state) has 7410 heating degree days and 273 cooling degree days.

In the 2010/2011 season, Nebraska's heating degree days totaled 6775 or 251 degree days more than the degree day normal. This indicates Nebraska's winter was 4 percent colder than normal. In 2011, Nebraska's cooling degree days totaled 950 or 58 degree days less than the degree day normal. This indicates Nebraska's summer was 6 percent cooler than normal. Comparison can also be made between degree day normals and degree days using individual months.

Heating Degree Days

Heating degree days measure how cold Nebraska is over a period of time relative to a base temperature (most commonly 65 degrees Fahrenheit). Heating degree days are used as an indicator of space heating energy requirements.

According to the graph and data table below, over the last forty years, 1999/2000 was the warmest year with 5406 heating degree days, and 1978/1979 was the coldest year with 7440 heating degree days. The graph below compares Nebraska's heating degree days each year (the blue line) to what is considered normal (the orange line).

The graph below compares heating degree days with the degree day normals for each month during the most recent year that data is available and the prior year. Heating degree days are usually found during the heating season, or winter, but there can be heating degree days during the fall and spring, too. Zero (0) degree days for any month indicate that temperatures reached levels that homes and businesses required minimal or no heating.

In 2009/2010, with the exception of August, the number of cooling degree days reported for each month was relatively the same as the normal number of cooling degree days. August was 26 percent warmer than normal with 347 cooling degree days versus 275 degree day normals. The total for 2010 indicated 6 percent warmer–than–normal summer weather.

In 2010/2011, with the exception of July, the number of cooling degree days reported for each month was below the normal number of cooling degree days. July was 25 percent warmer than normal with 420 cooling degree days versus 335 degree day normals. The total for 2011 indicated 6 percent cooler–than–normal summer weather.

Although January and February traditionally have the most heating degree days, the months of December and January normally have the most heating degree days in Nebraska. Nebraska had normal years in 2009/2010 and 2010/2011 when considering that the months of December and January had the most heating degree days.

Data in the table below shows that the number of heating degree days in January 2011 (1469) were 144 degree days above normal (1325). In other words, the weather was cooler than usual, and Nebraska consumers heated their homes and businesses 11 percent more than they would in a January with normal winter weather.

Cooling Degree Days

Cooling degree days measure how warm Nebraska is over a period of time relative to a base temperature (most commonly 65 degrees Fahrenheit). Cooling degree days are used as an indicator of air conditioning energy requirements.

According to the graph and data table below, over the last forty–one years, 1988 was the hottest year with 1285 cooling degree days, and 1992 was the coolest year with 628 cooling degree days. The year 2009 was the second–coolest year with 698 cooling degree days. The graph below compares Nebraska's cooling degree days each year (the blue line) to what is considered normal (the orange line). Note: The gap in the data occurs when no data was available.

The graph below compares cooling degree days with the degree day normals for each month during the most recent year that data is available and the prior year. Cooling degree days are usually found during the cooling season, or summer, but there can be cooling degree days during the fall and spring, too. With the exception of January 2006, the period from November to February of each year consistently has zero (0) cooling degree days in Nebraska. Zero (0) degree days for any month indicate that temperatures reached levels that homes and businesses required minimal or no cooling.

In 2010, with the exception of August and May, the number of cooling degree days reported for each month was relatively the same as the number of cooling degree days in a year with normal summer weather. August was 26 percent warmer than normal with 347 cooling degree days versus 275 degree day normals. May was 42 percent cooler than normal with 41 cooling degree days versus 71 degree day normals. The total for 2010 indicated 6 percent warmer–than–normal summer weather.

In 2011, with the exception of July, the number of cooling degree days reported for each month was below the normal number of cooling degree days. July was 25 percent warmer than normal with 420 cooling degree days versus 335 degree day normals. The total for 2011 indicated 6 percent cooler–than–normal summer weather.

July is traditionally the peak of summer. Out of all the months of the year, Nebraska had the most cooling degree days in the month of July in 2011, as observed in the graph above. In 2010, this was not the case. Nebraska had the most cooling days in the month of August (347) although July was very close with 338 cooling degree days.

Data in the table below again shows that the number of cooling degree days in July 2011 (420) was above normal (335). In other words, the weather was warmer than usual, and Nebraska consumers cooled their homes and businesses more than they would have if July's weather had been normal.

Conclusion

An increase on your utility bill could be related to an increase in degree days but, if you decide that weather had no bearing on the increase in your utility bill, other factors worth considering are changes in demand, changes in your building's structure, changes in the number of occupants, or changes in fuel prices.

This report was updated on April 26, 2012.
Typically, there is one month between updates.