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U.S. Climate Normals, 1971-2000 September 8, 2003 Order Now Product Availability NWS Inquiries Overview Products Historic Normals Frequently Asked Questions References Errata/Normals Updates Inventories Maps

1971-2000 Normals Product Suite

The 1971-2000 monthly and daily normals can be obtained by contacting NOAA's National Climatic Data Center (NCDC) as noted below. An on-line ordering system can be accessed by selecting 'Order Now' above.

Normals data are available in multiple formats. As indicated in Table 1 below, data can be obtained in easy-to-read PDF and/or ASCII formats. Alternatively, the companion digital data set can be ordered (charges apply). Please consult the digital data set documentation links below, and compare with the on-line ordering PDF samples to determine which format is more appropriate for you. As a rule of thumb, general users will find PDF/ASCII files more useful, while researchers and programmers will find the digital data sets more useful.

Orders can be placed by contacting NCDC.

Updated inventory of products: 1971-2000 Normals, Product Release Update [PDF].

1971-2000 normals team contacts:

Tom Whitehurst
Normals Project Leader
(828) 271-4349
Tom.Whitehurst@noaa.gov

Tim Owen
NWS Focal Point
(828) 271-4358
Tim.Owen@noaa.gov

National Weather Service Inquiries

Accessing the Data:

*** A NOAA.GOV domain name is required for data access ***

If you do not have this domain, please contact the NCDC Focal Point for NWS (see below) for a username/password.

1971-2000 monthly and daily normals are now available for National Weather Service offices. The monthly files can be obtained through an online web interface. In addition, both the monthly (Climatography of the United States No. 81) and daily (Climatography of the United States No. 84) files can be accessed at the following locations:

cdo.ncdc.noaa.gov/climatenormals/clim81 {Monthly Normals}
cdo.ncdc.noaa.gov/climatenormals/clim84 {Daily Normals}


For the monthly normals, files are listed by state (e.g., ALnorm.* refers to the normals files for Alabama). For the daily normals, files are listed by station using the cooperative network ID (e.g., AL010616.* refers to Beatrice, Alabama). Both ASCII (*.txt) and PDF-formatted publication (*.pdf) files are available for monthly normals. For first-order locations, PDF-formatted publication (*.pdf) files are available at the following location (note that files are identified using the cooperative network ID (e.g., 015550.pdf for Montgomery, Alabama):


cdo.ncdc.noaa.gov/climatenormals/clim84/PDF

Updates to the Normals: (see also Errata/Normals Updates)

Daily Normals (CLIM84) have been UPDATED. These updates are available on the web locations above. The updates primarily include changes to daily degree day values to harmonize with monthly totals. In the ASCII files, values of '-99' in the daily heating/cooling degree days represent values of 1 that have been determined to be 'spurious'. Such values are designated as spurious because of their separation from the major rise and fall of non-zero degree day values over the course of a heating/cooling degree day season, yet their presence assures consistency between the monthly total and the sum of the daily total (when values are considered equal to 1). For NWS offices, these changes have been distributed via AWIPS effective July 1, 2002 (along with the start of the new snow and heating degree day seasons).

These updated files supercede previously distributed normals. For PDF-formatted publications, please check the third page of an individual station PDF file for an updated release date of May 15, 2002 or later, as shown in the graphic below. Earlier versions should be disgarded.




Important Methodological Information:

Degree Day Totals:

The 1971-2000 normals have been provided to NWS HQ for implementation into the ASOS and AWIPS packages. The daily normals, temperature and precipitation values, when averaged or totaled for a given month, will yield the value presented in the monthly normals. This is also true for updated degree day totals.

Based on the input of the climate research community and energy groups, NCDC is computing monthly degree day totals DIRECTLY from daily average temperature values for first-order sites for the 1971-2000 period. NCDC has used a statistical technique (the H.C.S. Thom method) to ESTIMATE the monthly total. Generally, this approach closely agreed with the spline-fit daily values. However, the estimation often led to consistent under/overestimation of degree day totals when compared with observed values found in NCDC's Local Climatological Data. Stations with serially complete records were included in this approach, and are listed (see Degree Day Table) and with an asterisk ‘*' in the HDD/CDD section of the CLIM81 PDF publication.

Daily Leap Year Values:

In leap years, the values for February 28th should be used for February 29th, as no normals values are computed specifically for the leap year date.

Inhomogeneity Adjustments:

The following white paper (United States Climate Normals, 1971-2000: Inhomogeneity Adjustment Methodology) [PDF] is available regarding procedures for adjusting station data to account for inhomogeneities due to changes in station locations, instrumentation, time of observation, surrounding environment, observing practice, sensor drift, etc. The purpose of such adjustments is to produce a time series and normals statistics that are representative of the observing practices as of the end of the normals period (December 2000), since these are the conditions under which future observations will likely be compared.

Snow Normals

1971-2000 Snow Normals are being provided via AWIPS for use beginning with the 2002-2003 snow season. Please refer to the description in Table 1 above for details.

Snow normals, including snowfall, snow depth, and number of days with snowfall >= 0.1" and 1.0" can be obtained through an online web interface (see Table 1 above). The files can also be accessed at the following location:

http://cdo.ncdc.noaa.gov/climatenormals/clim20-02

Overview

Climate is an important factor in agriculture, commerce, industry, and transportation.  It affects many human activities such as farming, fuel consumption, structural design, building site location, trade, analysis of market fluctuations, and the utilization of other natural resources.  The influence of climate on our lives is endless. The National Oceanic and Atmospheric Administration's (NOAA's) National Climatic Data Center (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).

The mandate to describe the climate was combined with guidelines established through international agreement.  The United Nation's World Meteorological Organization (WMO) requires the calculation of normals every 30 years, with the latest covering the 1961-1990 period.  However, many WMO members, including the United States, update their normals at the completion of each decade. 

The average value of a meteorological element over 30 years is defined as a climatological normal. The normal climate helps in describing the climate and is used as a base to which current conditions can be compared.  Every ten years, NCDC computes new thirty-year climate normals for selected temperature and precipitation elements for a large number of U.S. climate and weather stations. These normals are summarized in daily, monthly, divisional, and supplementary normals products.

Products

1971-2000 U.S. Climate Normals Products Page

The 1971-2000 U.S. Climate Normals are summarized and published as four primary products:  Monthly (CLIM81), Daily (CLIM84), Divisional (CLIM85), and Supplemental (CLIM20). The normals also appear in several other products. Each product contains the normals appropriate for the application and users the product was designed for. Table 2 shows the element breakdown by publication.

Monthly Normals


The normals that are most commonly used are 30-year averages for precipitation and maximum, minimum, and mean temperature for each of the 12 months, plus an annual value. Monthly and annual average heating and cooling degree days are also important. The CLIM81 (Climatography of the United States No. 81) publication contains these monthly normals, plus monthly median precipitation and median mean temperature, for several thousand locations across the country.  There are two supplemental products associated with the CLIM81:  i.)  Supplement No. 1:  Monthly Precipitation Probabilities, and ii.) Supplement No. 2:  Annual Degree Days to Selected Bases.

Daily Normals


Daily normals are computed for National Weather Service offices, principal climatological stations, and cooperative network stations for the following six elements: precipitation, heating and cooling degree days, and maximum, minimum, and mean temperature. The daily station normals are summarized in the CLIM84 (Climatography of the United States No. 84) publication.

Divisional Normals


The contiguous United States, Alaska, Puerto Rico, and the U.S. Virgin Islands are divided into 360 geographical units called climate divisions. Monthly and annual divisional normals for mean temperature, precipitation, and heating and cooling degree days, as well as the corresponding standard deviation for these four elements, are published in the CLIM85 (Climatography of the United States No. 85) publication. Monthly and annual normals for the corresponding States and Territories, nine Census Regions, and national values for the contiguous United States, are derived from the divisional data and published in the Historical Climatology Series 4-1, 4-2, 4-3, 5-1, and 5-2 publications.

Supplemental Normals (CLIM20)


Normals statistics that have useful agricultural and other applications are published in the CLIM20 (Climatography of the United States No. 20) publication. These statistics include freeze date probabilities; normal growing degree days; monthly number of days with temperature, precipitation, and snowfall beyond various thresholds; monthly precipitation probabilities; temperature and precipitation "runs" statistics (consecutive number of days beyond various thresholds); and temperature, precipitation, and snowfall extremes, as well as the CLIM81 monthly normals.

The 1971-2000 normals will appear in several other NCDC publications, including the Local Climatological Data, Annual Summary; Comparative Climatic Data; Climatic Averages and Extremes for U.S. Cities; and the two supplements to the CLIM81 publication (Monthly Precipitation Probabilities and Annual Degree Days to Selected Bases).

Table 2
Climatic Elements and Statistics for the 1971-2000 Normals, by Product.

Element	Monthly	Daily	Divisional	Supplemental
Average Maximum Temperature	l	l		l
Average Minimum Temperature	l	l		l
Average Mean Temperature	l	l	l	l
Median Temperature	l
Standard Deviation of Mean Temperature	l		l
Extreme Maximum Temperature	l			l
Extreme Minimum Temperature	l			l
Freeze Date Probabilities				l
Average Heating Degree Days	l	l	l	l
Average Cooling Degree Days	l	l	l	l
Average Growing Degree Days				l
Standard Deviation of HDD	l		l
Standard Deviation of CDD	l		l
Average Precipitation	l	l	l	l
Median Precipitation	l			l
Standard Deviation of Precipitation	l		l
Extreme Precipitation	l			l
Precipitation Probabilities	l			l
Precipitation Quintiles	l
Mean Snowfall				l
Snowfall Quartiles				l
Extreme Snowfall				l
Days Exceeding Thresholds Values				l
Runs of Consecutive Days Beyond Thresholds				l

Historic Normals

Historic Normals Page

In the United States, normals have been computed for 1971-2000, 1961-1990, 1951-1980, 1941-1970, 1931-1960, and 1921-1950. The normals from 1931-1960 to present are digitally archived by NCDC. The 1921-1950 normals, which were the first normals set prepared according to WMO standards, were published in 1956 as Weather Bureau Technical Paper No. 31 (Monthly Normal Temperatures, Precipitation, and Degree Days). This technical paper is available from NCDC on microfiche.

These earlier normals have been summarized in previous editions of the CLIM81, CLIM84, CLIM85, and CLIM20 publications. In addition, a comprehensive Climate Atlas of the United States incorporates the 1961-1990 normals in a series of maps available in digital and hardcopy format; the 1951-80 freeze/frost probabilities have been summarized in a separate volume; and selected normals summaries have been collated into individual state volumes.

Frequently Asked Questions

When will the 1971-2000 normals be made available to the public?

NCDC will release the normals as indicated in the release schedule above in Table 1. 

How much will the normals products cost?

For current product prices, please contact NCDC at (828) 271-4800 (phone), orders@ncdc.noaa.gov (e-mail), or by writing to National Climatic Data Center, NOAA/NESDIS, Veach-Baley Federal Building, 151 Patton Ave., Asheville, NC 28801-5001.  

What is the period of record of the official normals and how often are they updated?

Normals cover a 30-year period of record, and are updated through the end of each decade ending in zero (e.g., 1951-1980, 1961-1990, etc.).  

What is the difference between Cooperative and First-Order stations?

Cooperative refers to weather stations that are part of the U.S. Cooperative Observing Network.  This network consists of several thousand temperature and/or precipitation stations that, in general, are manned by volunteer observers.  A subset of about one thousand of the longer-term stations from this network make up the U.S. Historical Climatology Network (U.S. HCN), which is a very important and celebrated network in the climate research community.

First-order refers to weather stations that are professionally maintained, primarily through the National Weather Service or Federal Aviation Administration.  Modernization of the National Weather Service during the 1990s resulted in the consolidation of many manned weather stations and the introduction of Automated Surface Observing System (ASOS) instrumentation throughout the United States.  ASOS instrumentation is now in use at the vast majority of first-order sites, which are primarily located at airports.

Both cooperative and first-order sites are essential to the 1971-2000 normals.  In many cases, cooperative sites offer a well-established, consistent observing site with periods of record that are continuous through the normals period.  First-order sites are the professionally manned sites with hourly observations.

Is it appropriate to use normals for predictive purposes?

Normals are best used as a base against which climate during the following decade can be measured. Comparison of normals from one 30-year period to normals from another 30-year period may lead to erroneous conclusions about climatic change. This is due to changes over the decades in station location, in the instrumentation used, in how weather observations were made, and in how the various normals were computed. The differences between normals due to these non-climatic changes may be larger than the differences due to a true change in climate.

What are the differences between normals, standard normals, and long-term means?

Normals refer to the official thirty-year normals computed by the National Climatic Data Center.  Standard normals are official normals computed for the World Meteorological Organization based on submission of data by its members.  Standard normals are computed every thirty years (e.g., 1931-1960, 1961-1990, etc.). Long-term means are mean values of meteorological elements that are computed for a myriad of reasons by organizations and individuals.  Even if long-term means are computed for the normals period (e.g., 1971-2000), only the NCDC values are appropriately called normals.

On What Output Media Are the Normals Available?

The 1931-1960 through 1971-2000 climate normals discussed on this home page are available as printed and digital publications, on microfiche, and/or digitally on magnetic tape. Please contact the NCDC Climate Services Division to determine the availability of any particular product, or if you have any questions. The Climate Services Division can be reached by telephone (828-271-4800), fax (828-271-4876), or via the internet: orders@ncdc.noaa.gov

All of the normals files in NCDC's digital archive (through the end of 1996) have been loaded onto one CD-ROM. This USDS - Vol. 1.0 CD-ROM contains only the documentation files and ASCII text data in the NCDC archive tape format; the data are not importable into a spreadsheet and the CD-ROM contains no software or extraction routines that allow users to import the data directly into spreadsheets or other applications. An updated CD-ROM product fo the 1971-2000 normals is planned for early 2002.

Digital ASCII data and PDF-formatted digital publications are available through NCDC's online store.

What is a “Climate Normal”?

The term climatic "normal" has faced a dilemma since its introduction a century and a half ago. A climate normal is defined, by convention, as the arithmetic mean of a climatological element computed over three consecutive decades (WMO, 1989).... a normal value is usually not the most frequent value nor the value above which half the cases fall." The casual user, however, tends to (erroneously) perceive the normal as what they should expect. Dr. Helmut E. Landsberg, who became Director of Climatology of the U.S. Weather Bureau in 1954 and, later, Director of the Environmental Data Service, summarized the dilemma quite well over four decades ago (Landsberg, 1955): "The layman is often misled by the word. In his every-day language the word normal means something ordinary or frequent. ...When (the meteorologist) talks about 'normal', it has nothing to do with a common event..... For the meteorologist the 'normal' is simply a point of departure or index which is convenient for keeping track of weather statistics..... We never expect to experience 'normal' weather."

It might be "normal" for the weather to swing radically between extremes from day to day and year to year, but the "climatic normal" is simply an arithmetic average of what has happened at such a "swinging" place. This is why it's important to use a measure of the variability of climate (such as the standard deviation and extremes) in conjunction with the climatic normal when studying the climate of a location (Guttman, 1989).

In accordance with national and international convention, the official climate normals computed for U.S. stations by NCDC consist of the arithmetic average of a meteorological element over 30 years. The ‘official’ normals are provided solely by NCDC, which should be noted in light of other non-official means computations from a myriad of sources.

Is a "Normal" the Climate You Would "Expect"?

Climate normals are a useful way to describe the average weather of a location. Several statistical measures are  computed as part of the normals, including measures of central tendency (such as the mean or median), of dispersion or how spread out the values are (such as the standard deviation or inter-quartile range), and of frequency or probability of occurrence.

Over the decades the term "normal", to the lay person, has come to be most closely associated with the mean or average.  In this context, a "climatic normal" is simply the arithmetic average of the values over a 30-year period (generally, three consecutive decades). A person unfamiliar with climate and climate normals may perceive the normal to be the climate that one should expect to happen.

It's important to note that the normal may, or may not, be what one would "expect" to happen. This is especially true with precipitation in dry climates, such as the desert southwestern region of the United States, and with temperature at continental locations which frequently experience large swings from cold air masses to warm air masses.

If the measuring equipment changes at a site, does that change the records?  Does it change the normals?

Changes at the site never change what was originally observed, but these observations are subject to edits based on established criteria. 

For normals, if the new equipment does not record weather elements in exactly the same way as the old, and causes a change in how weather is recorded relative to the previous instrumentation, then it does change the normals.  If the equipment MOVES, this will also often cause apparent changes in climate.  Location moves (anywhere from a few hundred feet to a few miles) can, in fact, cause greater changes than do instrumental changes.

The following white paper (United States Climate Normals, 1971-2000: Inhomogeneity Adjustment Methodology) [PDF] is available regarding procedures for adjusting station data to account for inhomogeneities due to changes in station locations, instrumentation, time of observation, surrounding environment, observing practice, sensor drift, etc. The purpose of such adjustments is to produce a time series and normals statistics that are representative of the observing practices as of the end of the normals period (December 2000), since these are the conditions under which future observations will likely be compared.  

Since climate fluctuates constantly, there are real changes in "normals" due to climate variations, and there are fake changes in "normals" due to artificial things like sensor changes, equipment moves, methodological issues, and so on.  The ONLY way to distinguish between fake and real variations is to have records from another piece of equipment at one site or the other that just keeps measuring the same way.

Are there differences in the values for the same time period between the 1961-1990 and 1971-2000 normals?

Differences in monthly values during the overlap period (1971-1990) in temperature and precipitation for a given station are possible due to differences in adjustment methods between the 1961-1990 and the 1971-2000 normals.  Generally, the 1971-2000 time series has been subjected to adjustments with combined spatial and statistical quality control, whereas the 1961-1990 time series was based less on spatial comparisons and more on limited quality control.  See the methdology section under the products page for more information on the 1971-2000 methodology.

How are degree day normals computed?

The following white paper (United States Climate Normals, 1971-2000: Degree Day Computation Methodology) [PDF] is available regarding the two-tiered approach to computing degree day normals.

The 1971-2000 degree day normals are computed using a new methodology. Previously, degree days were computed using the Thom rational conversion formulae (Thom, 1954, 1966). The Thom method allows a monthly degree day total to be estimated from input average temperature means and standard deviations.

For the 1971-2000 normals, degree day totals were computed in two distinct ways. For stations that are not first-order National Weather Service locations, the rational conversion formulae developed by Thom (1954, 1966) was modified by using inputs of daily spline-fit (rather than monthly) means and standard deviations of average temperature. This modification improved consistency of the estimated degree day totals by eliminating monthy-by-month 'steps' in the inputs. For first-order stations, where daily data sets are largely devoid of missing values, monthly degree day totals were derived directly from daily values.

What are 'spurious' degree day values in the daily normals?

In the daily normals files, values of '-99' (or an asterisk in non-digital printouts) in the daily heating/cooling degree days represent values of 1 that have been designated to be 'spurious'. Such values are designated as spurious because of their separation from the major rise and fall of non-zero degree day values over the course of a heating/cooling degree day season, yet their presence assures consistency between the monthly total and the sum of the daily total (when values are considered equal to 1).

References

Baker, D.G., 1975: Effect of observation time on mean temperature calculation. Journal of Applied Meteorology, vol. 14, pp. 471-476.

Crutcher, H.L., G.F. McKay, and D.C. Fulbright, 1977: “A Note on a Gamma Distribution Computer Program and Computer Produced Graphs”, NOAA Technical Report EDS 24, Washington, U.S. Government Printing Office.

Crutcher, H.L. and R.L. Joiner, 1978: “Gamma Distribution Bias and Confidence Limits”, NOAA Technical Report EDIS 30, Washington, U.S. Government Printing Office.

Easterling, D.R, and T.C. Peterson, 1995: A new method for detecting and adjusting for undocumented discontinuities in climatological time series. Internation. Journal of Climatology, vol. 15, pp. 369-377.

Greville, T.N.E., 1967: "Spline functions, interpolation, and numerical quadrature," Mathematical Methods for Digital Computers, Vol. II, A. Ralston and H.S. Wilf (eds.), pp.156-168, Wiley, New York.

Guttman, N.B. and M.S. Plantico, 1987: “Climatic Temperature Normals”, Journal of Climate and Applied Meteorology, vol. 26, pp. 1428-1435.

Guttman, N.B., 1989:  "Statistical descriptors of climate," Bulletin of the American Meteorological Society, Vol. 70, pp. 602-607.

Guttman, N.B. and R.G. Quayle, 1995:  "A Historical Perspective of U.S. Climate Divisions", Bulletin of the American Meteorological Society, Statistical descriptors of climate, Bulletin of the American Meteorological Society, Vol. 77, no. 2, pp. 293-303.

Karl, T.R., C.N. Williams, Jr., P.J. Young, and W.M. Wendland,1986:  "A model to estimate the time of observation bias associated with monthly mean maximum, minimum, and mean temperatures for the United States," Journal of Climate and Applied Meteorology, Vol. 25, pp. 145-160.

Karl, T.R., and C.N. Williams, Jr., 1987:  "An approach to adjusting climatological time series for discontinuous inhomogeneities," Journal of Climate and Applied Meteorology, Vol. 26, pp. 1744-1763.

Karl, T.R., C.N. Williams, Jr., F.T. Quinlan, and T.A. Boden, 1990: "United States Historical Climatology Network (HCN) Serial Temperature and Precipitation Data," Oak Ridge National Laboratory Environmental Sciences Division Publication No. 3404 (ORNL/CDIAC-30, NDP-019/R1), 377 pages.

Landsberg, H.E., 1955:  "Weather 'normals' and normal weather," Weekly Weather and Crop Bulletin, 1/31/55, pp. 7-8.

Peterson, T.C., and D.R. Easterling, 1994: Creation of homogeneous composite climatological reference series. Internation Journal of Climatology, vol. 14, pp. 671-679.

Peterson,T.C., R. Vose, R. Schmoyer, and V. Razuvaev, 1998: Global Historical Climatology Network (GHCN) quality control of monthly temperature data. International Journal of Climatology, vol. 18, pp. 1169-1179.

Reek, T., S.R. Doty, and T.W. Owen, 1992:  "A deterministic approach to the validation of historical daily temperature and precipitation data from the Cooperative Network," Bulletin of the American Meteorological Society, Vol. 73, pp. 753-762.

Steurer, P., 1985:  "Creation of a serially complete data base of high quality daily maximum and minimum temperatures." Unpublished technical note available from the Global Climate Laboratory, NCDC.

Thom, H.C.S., 1952:  "Seasonal degree-day statistics for the United States," Monthly Weather Review, Vol. 80, pp. 143-149.

Thom, H.C.S., 1954:  "The rational relationship between heating degree days and temperature," Monthly Weather Review, Vol. 82, pp. 1-6. [PDF Copy]

Thom, H.C.S., 1959:  "The distribution of freeze-date and freeze-free period for climatological series with freezeless years," Monthly Weather Review, Vol. 87, pp. 136-144.

Thom, H.C.S., 1966:  "Normal degree days above any base by the universal truncation coefficient," Monthly Weather Review, Vol. 94, pp. 461-465. [PDF Copy]

Thom, H.C.S. and R.H. Shaw, 1958:  "Climatological analysis of freeze data for Iowa," Monthly Weather Review, Vol. 86, pp. 251-257.

U.S. Department of Commerce, Bureau of the Census, 1991: 1990 Census of Population and Housing, Summary of Population and Housing Characteristics, Puerto Rico.

U.S. Department of Commerce, Bureau of the Census, 1992: 1990 Census of Population, General Population Characteristics, Series CT-1 (Alabama through Wyoming and U.S. Summary).

Vestal, C.K., 1971:  "First and last occurrences of low temperatures during the cold season," Monthly Weather Review, Vol. 99, pp. 650-652.

World Meteorological Organization, 1989:  Calculation of Monthly and Annual 30-Year Standard Normals, WCDP-No. 10, WMO-TD/No. 341, Geneva: World Meteorological Organization.

Errata/Normals Updates

Corrections to 1971-2000 Normals
Last Updated: February 1, 2003

Normals files have been updated. Monthly normals released on or after March 4, 2002 are current. Daily normals released on or after May 9, 2002 are current. Please check the digital date stamp on the files that you may have previously obtained to determine if an update is needed. NCDC will provide update files by request at no charge. The present versions of the normals have been implemented by the National Weather Service for official use beginning July 1, 2002.

Normals Updates by Date:

01/25/02: Updated WMO Flag
The WMO qualification flag (FLAG 2; '+') has been updated for ALL stations. The flag now correctly identifies whether a station meets WMO standards for data completeness (indicated with a '+'). WMO qualification requires a station to have no more than three consecutve year-month values missing for a given month or no more than five overall values missing for a given month (out of 30 values).

02/14/02: Updated Normals CD
The U.S. Climate Normals CD (including PDF/ASCII files) has been updated for selected states to correct data formatting for a number of ASCII files. Present distributions from NCDC incorporate all individual value changes.

01/25/02: Selected changes have been made to the monthly normals. These changes correct a small discrepancy in rounding for some first-order stations, as well as the wholesale changes for Denver International Airport (DEN) (using Stapleton Airport (COOP ID 052220)) at the request of NWS.

02/14/02: Selected changes have been made to the monthly normals. These correct a deficiency in the estimation of degree day totals that primarily impact values around the minimum month of the respective degree day season. The typical change impacts one month (and the accompanying annual value) for a given station. About 1% of all degree day monthly values are impacted.

04/15/02: Annual Extreme Values/Years
The annual extreme values/years have been computed to be the maximum/minimum occurrence for the thirty annual values from 1971-2000, rather than for the twelve monthly values. This update is provided for all stations in the attached Annual Extremes file. The file format is as follows: Column 1= Station Number; Column 2= Element Code (1: Minimum Temperature, 2: Maximum Temperature, 3: Average Temperature, 4: Total Precipitation; Column 3: 30-year Annual Extreme Value (units: degrees F to tenths for temperature, hundredths of an inch for precipitation); Column 4: Latest year of occurrence for extreme value, # after year indicates multiple occurrences of value.

05/9/02: Daily Normals
The daily normals have been released in ASCII format. This release assures consistency between daily, monthly, and annual values, particularly for degree days. The release also assures a smooth day-to-day change in daily values. In the ASCII files, values of '-99' in the daily heating/cooling degree days represent values of 1 that have been designated to be 'spurious'. Such values are designated as spurious because of their separation from the major rise and fall of non-zero degree day values over the course of a heating/cooling degree day season, yet their presence assures consistency between the monthly total and the sum of the daily total (when values are considered equal to 1). This release of the daily normals is consistent with monthly normals released in early March, 2002.

The National Weather Service implemented normals values in December, 2001 for temperature, precipitation, and cooling degree days. Releases of the normals since that time have resulted in a small number of changes in the month values that were released at that time. NCDC has summarized these differences in the attached NWS Monthly Normals Update Table, which lists the changes by station call sign, element, month, old value, new value, and difference, respectively. This table includes values for cooling degree days and precipitation for the first six months of the year only, since there were no changes in temperature, heating degree days have not yet been implemented, and the updated values will be implemented beginning July 1, 2002. These changes, albeit limited in scope and size, can have an impact on accumulated statistics.

08/07/02: First-Order Daily PDF Files
An update to selected Daily PDF files was made to correct negative degree day totals for October whenever asterisk daily values were present in that month. This correction was for selected monthly (October), seasonal (Autumn), and annual totals of CDD (or, in very few cases, HDD). No other months or elements were impacted. ASCII and other digital data set files were NOT impacted. The PDF files were corrected and placed on the cdo server under the /clim84/PDF subdirectory. Corrected files can be differentiated from earlier versions by the presence of an asterisk following 'May 15, 2002' in the release date in the corner of page 3. About 15% of PDF station files required correction, including the following station numbers: 045983,064767,083186,086628,087886,088788,101303,119029,135198,135235,137844,176905,190736,191386,195159,
200164,203858,203936,204150,205712,207227,208251,216835,217004,217294,240807,243558,243751,243996,256040,
262708,266779,271683,293682,294856,300042,300687,306820,308383,308737,309005,322859,323616,350328,352709,
356546,357500,360130,362260,390020,396937,425186,425654,431081,457938,462718,472428,472839,473269,474821,
474961,476330,478968,479335

01/15/03: Corrected Value for Milton, MA (Blue Hill Observatory)
The precipitation value for December 08, 2000 was changed from 1.16" to 0.06". This change impacted the December precipitation normal value, changing it from 4.56" to 4.53". Likewise, the annual precipitation normal changed from 51.22" to 51.19".

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