NOAA's 1981-2010 Climate Normals


NOAA's National Climatic Data Center (NCDC) released the 1981-2010 Normals on July 1, 2011. Climate Normals are the latest three-decade averages of climatological variables, including temperature and precipitation. This new product replaces the 1971-2000 Normals product. Additional Normals products; such as frost/freeze dates, growing degree days, population-weighting heating and cooling degree days, and climate division and gridded normals; will be provided in a supplemental release by the end of 2011.


Obtaining the 1981-2010 Climate Normals


Users can access the 1981-2010 Climate Normals via ftp or http. It is highly recommended that users first download and read the readme.txt file which describes all file information and where each file is located.


Pre-release Webcast


NCDC hosted a webcast on June 13, 2011 with over 150 participants. This webcast focused on what users can expect to see when the 1981-2010 Climate Normals are released on July 1, 2011. Presentation materials for this webcast are available here:

Normals-Webcast-061311.pdf

For more information on this webcast, such as viewing a recorded version of the webcast, please contact Robin Evans.


FAQs

  1. What are Normals?
  2. When will the 1981 - 2010 Normals be available?
  3. What are considered "core" Normals?
  4. What are "supplemental" Normals?
  5. Why does NOAA produce Normals?
  6. What are Normals used for?
  7. What changes are being made in the computation of the 1981 - 2010 Normals versus previous versions?
  8. What qualifies or disqualifies a station to be included in Normals products?
  9. How many stations will be included in the normals?
  10. What do climate Normals tell us about global warming or climate change?
  11. What portion of the difference from the new Normals and the previous Normals was due to climate change?
  12. How can I obtain historic Normals from previous Normal periods?
  13. What are Heating and Cooling Degree Days? What are Growing Degree Days?
  14. How can I obtain Heating and Cooling Degree Day Normals set to different base temperatures? And for Growing Degree Units?
  15. How can I obtain hourly, daily, and monthly Normals for additional weather elements such as dew point, sea level pressure, and wind?
  16. How does the transition to ASOS affect the computation of Normals?
  17. How do the Normals compare to Alternative Normals and Dynamic Normals?
  18. NOAA's Climate Prediction Center has already changed their Normals to the 1981 - 2010 base period? Why are those Normals not available?
  1. What are Normals?

    In the strictest sense, a "normal" of a particular variable (e.g., temperature) is defined as the 30-year average. For example, the minimum temperature normal in January for a station in Chicago, Illinois, would be computed by taking the average of the 30 January values of monthly-averaged minimum temperatures from 1981 to 2010. Each of the 30 monthly values was in turn derived from averaging the daily observations of minimum temperature for the station. In practice, however, much more goes into NCDC's Normals product than simple 30-year averages. Procedures are put in place to deal with missing and suspect data values. In addition, Normals include quantities other than averages such as degree days, probabilities, standard deviations, etc. Normals are a large suite of data products that provide users with many tools to understand typical climate conditions for thousands of locations across the United States. (top)

  2. When will the 1981 - 2010 Normals be available?

    The new Normals are being made available in two releases. Core Normals were released on July 1, 2011. Supplemental Normals will be available by January 2012. Initial access to both releases will be via file transfer protocol (FTP). We expect to provide more advanced (and user-friendly) Web services and selection capabilities to the new Normals from NCDC's Web site by November 2011 for the core Normals and April 2012 for the supplemental Normals. (top)

  3. What are considered "core" Normals?

    The core 1981 - 2010 Normals are the most-widely used Normals as identified by NCDC in close consultation with the National Weather Service (NWS) and a wide array of climate data users. Specifically, core Normals refer to the daily and monthly station-based Normals of temperature, precipitation, snowfall, snow depth, and heating and cooling degree days. Generally, this coincides with the key products produced for each observation station called CLIM81 and CLIM84 released for the 1971 - 2000 Normals (except for snowfall and snow depth Normals). (top)

  4. What are "supplemental" Normals?

    Supplemental Normals are a catchall category for all Normals products that will not be released in the core Normals release. An example is our population-weighted degree day normals product, which cannot be computed until the U.S. Census Bureau releases its final population figures. (top)

  5. Why does NOAA produce Normals?

    NOAA's computation of climate Normals is in accordance with the recommendation of the World Meteorological Organization (WMO), of which the United States is a member. While the WMO mandates each member nation to compute 30-year averages of meteorological quantities at least every 30 years (1931 - 1960, 1961 - 1990, 1991 - 2020, etc.), the WMO recommends a decadal update, in part to incorporate newer weather stations. Further, NOAA's NCDC has a responsibility to fulfill the mandate of Congress "... to establish and record the climatic conditions of the United States." This responsibility stems from a provision of the Organic Act of October 1, 1890, which established the Weather Bureau as a civilian agency (15 U.S.C. 311). (top)

  6. What are Normals used for?

    Meteorologists and climatologists regularly use Normals for placing recent climate conditions into a historical context. NOAA's Normals are commonly seen on local weather news segments for comparisons with the day's weather conditions. In addition to weather and climate comparisons, Normals are utilized in seemingly countless applications across a variety of sectors. These include: regulation of power companies, energy load forecasting, crop selection and planting times, construction planning, building design, and many others. (top)

  7. What changes are being made in the computation of the 1981 - 2010 Normals versus previous versions?

    Several changes and additions have been incorporated into the 1981-2010 Normals. Monthly temperature and precipitation normals are based on underlying data values that have undergone additional quality control. Monthly temperatures have also been standardized to account for the effects of station moves, changes in instrumentation, etc. These enhancements are described in more detail in the following peer-reviewed papers:
    ftp://ftp.ncdc.noaa.gov/pub/data/ushcn/v2/monthly/menne-etal2009.pdf
    and
    ftp://ftp.ncdc.noaa.gov/pub/data/ushcn/v2/monthly/menne-williams2009.pdf

    Unlike the 1971-2000 Normals, daily data were used extensively in the computation of daily temperature and precipitation normals as well as heating and cooling degree day normals, providing greater precision of intra-seasonal features. In previous installments, daily precipitation normals were computed as a spline fit through the monthly values. For 1981-2010, this metric will be replaced with a suite of metrics, including daily probabilities of precipitation as well as month-to-date and year-to-date precipitation normals. New products in the 1981-2010 Normals include normals derived from hourly data values. More details can be found in Arguez et al. 2011 which can be accessed here:
    ftp://ftp.ncdc.noaa.gov/pub/data/aarguez/Normals/1981-2010/Arguez-Extended-Normals-AMS2011.pdf (top)

  8. What qualifies or disqualifies a station to be included in Normals products?

    Normals are computed for as many NWS stations as reasonably possible. Some stations do not have sufficient data over the 1981 - 2010 period to be included in Normals, and this is the primary reason a station may not be included. Normals are computed for stations that are part of the NWS's Cooperative Observer Program (COOP) Network. Some additional stations are included that have a Weather Bureau -- Army -- Navy (WBAN) station identification number including the Climate Reference Network (CRN). Normals are only computed for stations in the United States (including Alaska and Hawaii) as well as U.S. territories, commonwealths, compact of free association nations, and one Canadian CRN station. (top)

  9. How many stations will be included in the normals?

    The 1981-2010 Climate Normals includes normals for over 9800 stations. Temperature-related normals are reported for 7500 stations and precipitation normals are provided for 9300 stations, including 6400 that also have snowfall normals and 5300 that have normals of snow depth. (top)

  10. What do climate Normals tell us about global warming or climate change?

    Normals were not designed to be metrics of climate change. In fact, when the widespread practice of computing Normals commenced in the 1930s, the generally-accepted notion of the climate was that underlying long-term averages of climate time series were constant. Changes from one installment of Normals to the next do, nonetheless, provide some evidence of climate change impacts. However, care must be taken when interpreting changes between one Normals period and the other. Differences between the reported 1971-2000 Normals and the 1981-2010 Normals may be due to station moves, changes in methodology, changes in instrumentation, etc. that are not reflective of real changes in the underlying climate signal. Rather than inferring climate change impacts from Normals, we recommend users instead look at trends in U.S. Historical Climatology Network (USHCN) time series:
    http://www.ncdc.noaa.gov/oa/climate/research/ushcn (top)

  11. What portion of the difference from the new Normals and the previous Normals was due to climate change?

    Compared to the previous Normals, the new Normals includes the decade of the 2000s and loses the decade of the 1970s. As the 2000s were warmer than the 1970s, this has had a warming influence on the Normals. Comparing these decades using our best data set for climate change analysis, the USHCN, we find that the decade of the 2000s was about 1.5F warmer than the 1970s. For maximum, minimum and mean temperature the difference, respectively, was 1.37F, 1.55F and 1.46F. As the Normals are an average of three decades, this would warm the new Normals by approximately 0.5F. The difference between these values and the actual difference between the reported 1971-2000 Normals and the new Normals are caused by station moves, changes in observing practices or instruments, etc. (top)

  12. How can I obtain historic Normals from previous Normal periods?

    To obtain 1961 - 1990 climate Normals or earlier versions, please contact NCDC's User Engagement & Services Branch. (top)

  13. What are Heating and Cooling Degree Days? What are Growing Degree Days?

    Heating and cooling degree days are metrics of energy demand associated with the variation of mean temperature across space and time. Growing degree days are metrics of agricultural output, also as a function of mean temperature. The computation of degree days involves certain threshold temperatures, e.g., 65°F for heating and cooling degree days. These thresholds are referred to as base temperatures. (top)

  14. How can I obtain Heating and Cooling Degree Day Normals set to different base temperatures? And for Growing Degree Units?

    While NCDC utilizes 65°F as the base temperature for the standard calculation of heating and cooling degree days, NCDC's climate normal products include alternative computations of heating and cooling degree days for various base temperatures. In addition, growing degree days are computed for various crop-specific base temperatures. Please contact NCDC's User Engagement & Services Branch for more information. (top)

  15. How can I obtain hourly, daily, and monthly Normals for additional weather elements such as dew point, sea level pressure, and wind?

    The vast majority of weather stations utilized in Normals only routinely report air temperature and precipitation. A smaller set of stations have fairly complete records of additional variables such as dew point temperature, sea level pressure, and wind speed and direction. For 262 first order stations, we provide hourly normals of temperature, dew point temperature, heat index, wind chill, heating and cooling degree hours, sea level pressure, and wind. (top)

  16. How does the transition to ASOS affect the computation of Normals?

    Automated Surface Observing System (ASOS) stations were implemented in the mid-1990s, largely replacing human observers. As a result, there are inhomogeneities in the 1981-2010 underlying data records due to changes in observing practices. These inhomogeneities are accounted for to the extent possible by quality control and the standardization of monthly temperature values. See the Menne et al. (2009) and Menne and Williams (2009) for more information. (top)

  17. How do the Normals compare to Alternative Normals and Dynamic Normals?

    In response to observed climate change, NOAA's NCDC has been investigating a suite of experimental products that attempt to provide a better estimate of "normal" than the traditional 30-year average Normals of temperature and precipitation. This project is known as Alternative Normals. This project is parallel to the computation of NOAA's official 1981 - 2010 Normals and is ongoing. There are no plans to discontinue the computation of official Normals every ten years in response to results obtained from the Alternative Normals project. For more information on Alternative Normals, please contact NCDC's Anthony Arguez. Dynamic Normals refers to a tool available on NCDC's Web site that allows users to create their own Normals for a particular station by selecting customized start and end years for the averages. This tool has not been updated since 2001 and there are no plans to update this tool in the foreseeable future. For more information on Dynamic Normals, please contact NCDC's User Engagement & Services Branch. (top)

  18. NOAA's Climate Prediction Center has already changed their Normals to the 1981 - 2010 base period? Why are those Normals not available?

    Many organizations, including NOAA's Climate Prediction Center (CPC), develop their own averages and change base periods for internal use. However, NCDC's climate Normals are the official United States Normals as recognized by the World Meteorological Organization and the main Normals made available for a variety of variables. Below is a brief summary of changes to the CPC products due to the change in climate base period from 1971 - 2000 to 1981 - 2010:

    Climate Monitoring:
    • In January 2011, the CPC completed development of new climate normals based on the 1981 - 2010 period. This effort was done for all of the Climate Data Assimilation System (CDAS) and Global Ocean Data Assimilation (GODAS) data products that are used for real-time monitoring of the global climate system.
    • This new climate base period was used to prepare numerous operational climate monitoring products, including the Climate Diagnostics Bulletin (CDB) and ocean monitoring products in February 2011. For example, the CDB and ocean products released in February 2011 that describe conditions during January, 2011 use climate anomalies based on the new climate base period.
    • A notification of this change to the CPC normals was placed on the CPC website prior to the change in January 2011.

    Climate Prediction:
    • CPC normals for stations and climate divisions, which are used in CPC's operational forecasts, will be officially updated in mid-May.
    • CPC normals for heating and cooling degree days will be updated in mid-June. (top)


Changes in Normals


When comparing the 1981-2010 Normals to the 1971-2000 Normals computed using the same methodology, both maximum temperatures and minimum temperatures are about 0.5F warmer on average in the new normals. The averaged annual statewide changes in maximum and minimum temperatures are shown in Figures 1 and 2, respectively.

Figure 1 Figure 2

Contact


For general questions about Normals or help accessing the 1971 - 2000 product, please contact NCDC's User Engagement & Services Branch at 828-271-4800, option 2. For questions regarding the development of the 1981 - 2010 Normals, please contact Anthony Arguez.