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Long-Term Daily Climate Records from Stations Across the Contiguous United States

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Investigators

M.J. Menne, C.N. Williams, Jr., and R.S. Vose
National Climatic Data Center, National Oceanic and Atmospheric Administration

Table of Contents

Introduction

The United States Historical Climatology Network (USHCN) is essentially a subset of the U.S. Cooperative Observer Network operated by NOAA's National Weather Service (NWS). The approximately 1200 USHCN stations were originally selected according to factors such as record longevity, percentage of missing values, spatial coverage as well as the number of station moves and/or other station changes that may affect data homogeneity. Most USHCN stations are situated in rural areas or small towns; however, a smaller number of stations are also part of the NOAA NWS synoptic network, whose stations are generally located at airports in more urbanized environments. USHCN datasets have been developed at NOAA's National Climatic Data Center (NCDC) in collaboration with the Department of Energy's Carbon Dioxide Information Analysis Center (CDIAC).

The USHCN project dates to the mid-1980s (Quinlan et al. 1987). At that time, in response to the need for an accurate, unbiased, modern historical climate record for the United States, personnel at the Global Change Research Program of the U.S. Department of Energy and at NCDC defined a network of 1219 stations in the contiguous United States whose observation would comprise a key baseline dataset for monitoring U.S. climate. Since then, the USHCN monthly dataset has been updated several times (e.g., Karl et al., 1990; Easterling et al., 1996). The USHCN Version 2 Serial Monthly data release is the most recent update to the USHCN datasets.

The first database released by NCDC to contain daily data from USHCN stations, the HCN/Daily (HCN/D; Hughes et al. 1992; hereafter H92), contained daily maximum and minimum temperatures and precipitation totals from 138 select U.S. stations. The temperature and precipitation records from these stations were considered to be the most reliable, internally consistent, and unbiased records from the USHCN. These records were compiled from digital and nondigital data sets archived at NCDC that come from a variety of sources, including climatological publications, universities, federal agencies, individuals, and data archives. Records were subjected to extensive manual and automated quality assurance (QA) checks. The selection of stations for inclusion in H92 was performed with the following data quality issues in mind.

  • The degree to which each station maintained a constant observation time for maximum and minimum temperatures, excursions from a station's predominant observing time of no more than four years being desired.
  • At least 95% of a station's pre-1951 data should be contained in NCDC digital daily archives.
  • A station's potential for heat island bias over time should be low.
  • Quality assessments based upon the decile ranking assigned by Karl et al. (1990) to the stations' monthly maximum/minimum temperature data for certain quality characteristics.

Since the release of H92, much more work has been conducted at NCDC involving compilation and digitizing of daily data. However, to enable the compilation of a database providing better spatial coverage of the contiguous United States, the four station selection criteria listed above were not strictly adhered to in later versions of the USHCN daily database (e.g., Williams et al. 2004).

The USHCN daily data contain observations of maximum and minimum temperature, precipitation amount (liquid equivalent), snowfall amount, and snow depth. Records from about 700 stations begin before 1900 and most station records are essentially complete for at least 60 years extending through a recent year. It's common for temperature and precipitation records to have started earlier than snowfall and snow depth measurements, especially at stations with longer periods or record.

Data Sources and Compilation

The current version of the USHCN Daily database contains the same variables, and was subjected to the same quality control checks (details below), as NCDC's Global Historical Climatology Network-Daily (GHCN-Daily) database. USHCN-Daily is in fact a subset of GHCN-Daily, which serves as the official archive for daily data from the Global Climate Observing System (GCOS) Surface Network (GSN). Following is a list of the sources of data currently contained in USHCN-Daily along with a brief description of each source.

  • U.S. Cooperative Summary of the Day (NCDC DSI-3200) - Includes daily observations at 19,000 stations in the United States and its territories. While most measurements are taken by volunteer observers as part of the U.S. NOAA National Weather Service's Cooperative Observer (COOP) Program, manual and automated measurements from some "First Order" sites are also included. Some records extend back to the late 1800s, but most do not begin until 1948 or later.
  • CDMP U.S. Cooperative Summary of the Day (NCDC DSI-3206) - Contains mostly pre-1948 observations from more than 11,000 COOP stations that were keyed as part of NCDC's Climate Data Modernization Program (CDMP).
  • U.S. First Order Summary of the Day (NCDC DSI-3210) - Contains historical and present-day manual and automated observations from approximately 1600 sites, including U.S. First Order stations, a selection of Canadian sites, and U.S.-operated stations in other countries.

Quality Control

As part of the GHCN-Daily quality control procedures, USHCN-Daily data have been subjected to a variety of internal consistency, frequent-value, outlier, and spatial consistency checks. The quality control efforts are always improving and expanding, so users are urged to keep up with them by visiting the Quality Control section of the NCDC/GHCN website.

Bias Adjustments

At present, the USHCN daily data contain no adjustments for biases resulting from historical changes in instrumentation and observing practices. This is true of the GHCN-Daily database as a whole, which includes the USHCN daily data. However, there is ongoing work at NCDC to develop adjustments that can be applied to daily maximum and minimum temperatures, and a GHCN daily derived product containing adjusted daily temperatures may become available in the future.

Station Information

The format of each record in the USHCN Daily station inventory file (ushcn-stations.txt) is as follows.

Variable Columns Type
COOP ID 1-6 Character
LATITUDE 8-15 Real
LONGITUDE 17-25 Real
ELEVATION 27-32 Real
STATE 34-35 Character
NAME 37-66 Character
COMPONENT 1 68-73 Character
COMPONENT 2 75-80 Character
COMPONENT 3 82-87 Character
UTC OFFSET 89-90 Integer

These variables have the following definitions:

COOP ID   is the U.S. Cooperative Observer Network station identification code. Note that the first two digits in the Coop ID correspond to the assigned state number (see Table 1 below).
LATITUDE   is latitude of the station (in decimal degrees).
LONGITUDE   is the longitude of the station (in decimal degrees).
ELEVATION   is the elevation of the station (in meters, missing = -999.9).
STATE   is the U.S. postal code for the state.
NAME   is the name of the station location.
COMPONENT 1   is the Coop Id for the first station (in chronologic order) whose records were joined with those of the USHCN site to form a longer time series. "------" indicates "not applicable".
COMPONENT 2   is the Coop Id for the second station (if applicable) whose records were joined with those of the USHCN site to form a longer time series.
COMPONENT 3   is the Coop Id for the third station (if applicable) whose records were joined with those of the USHCN site to form a longer time series.
UTC OFFSET   is the time difference between Coordinated Universal Time (UTC) and local standard time at the station (i.e., the number of hours that must be added to local standard time to match UTC).

TABLE 1. State numbers and abbreviations for the contiguous United States.

State number State abbreviation State
01 AL Alabama
02 AZ Arizona
03 AR Arkansas
04 CA California
05 CO Colorado
06 CT Connecticut
07 DE Delaware
08 FL Florida
09 GA Georgia
10 ID Idaho
11 IL Idaho
12 IN Indiana
13 IA Iowa
14 KS Kansas
15 KY Kentucky
16 LA Louisiana
17 ME Maine
18 MD Maryland
19 MA Massachusetts
20 MI Michigan
21 MN Minnesota
22 MS Mississippi
23 MO Missouri
24 MT Montana
25 NE Nebraska
26 NV Nevada
27 NH New Hampshire
28 NJ New Jersey
29 NM New Mexico
30 NY New York
31 NC North Carolina
32 ND North Dakota
33 OH Ohio
34 OK Oklahoma
35 OR Oregon
36 PA Pennsylvania
37 RI Rhode Island
38 SC South Carolina
39 SD South Dakota
40 TN Tennessee
41 TX Texas
42 UT Utah
43 VT Vermont
44 VA Virginia
45 WA Washington
46 WV West Virginia
47 WI Wisconsin
48 WY Wyoming

Data Files

USHCN data files may be downloaded from CDIAC's anonymous FTP area (see the USHCN Data Access page).

There are 48 state files (ASCII) using the following naming convention: stateno_stateabbrev.txt.gz.

Example: state01_AL.txt.gz.

station_file_format.txt contains ASCII file format information and variable definitions.

There are also five NetCDF files containing data organized by variable type (e.g., ushcn_prcp.nc.gz).

ushcn-stations.txt contains a listing of all of the stations along with their latitude and longitude.

us.txt.gz contains data for the 48 states represented.

The format of each record in an ASCII data file, be it a state-level file (e.g., state01_AL.txt) or the file for the entire U.S. (us.txt) is as follows. (Each record in a file contains one month of daily data.)

Variable Columns Type
COOP ID 1-6 Character
YEAR 7-10 Integer
MONTH 11-12 Integer
ELEMENT 13-16 Character
VALUE1 17-21 Integer
MFLAG1 22 Character
QFLAG1 23 Character
SFLAG1 24 Character
VALUE2 25-29 Integer
MFLAG2 30 Character
QFLAG2 31 Character
SFLAG2 32 Character
VALUE31 257-261 Integer
MFLAG31 262 Character
QFLAG31 263 Character
SFLAG31 264 Character

These variables have the following definitions:

COOP ID   is the U.S. Cooperative Observer Network station identification code. Note that the first two digits in the Coop Id correspond to the state.
YEAR   is the year of the record.
MONTH   is the month of the record.
ELEMENT   is the element type. There are five possible values:
    PRCP = precipitation (hundredths of inches)
    SNOW = snowfall (tenths of inches)
    SNWD = snow depth (inches)
    TMAX = maximum temperature (degrees F)
    TMIN = minimum temperature (degrees F)
VALUE1   is the value on the first day of the month (missing = -9999).
MFLAG1   is the measurement flag for the first day of the month. There are five possible values:
    Blank = no measurement information applicable
    B = precipitation total formed from two 12-hour totals
    D = precipitation total formed from four six-hour totals
    H = represents highest or lowest hourly temperature
    L = temperature appears to be lagged with respect to reported hour of observation
    P = identified as "missing presumed zero" in DSI 3200 and 3206
    T = trace of precipitation, snowfall, or snow depth
QFLAG1   is the quality flag for the first day of the month. There are fourteen possible values:
    Blank = did not fail any quality assurance check
    D = failed duplicate check
    G = failed gap check
    I = failed internal consistency check
    K = failed streak/frequent-value check
    L = failed check on length of multiday period
    M = failed megaconsistency check
    N = failed naught check
    O = failed climatological outlier check
    R = failed lagged range check
    S = failed spatial consistency check
    T = failed temporal consistency check
    W = temperature too warm for snow
    X = failed bounds check
    Z = flagged as a result of an official Datzilla investigation
SFLAG1   is the source flag for the first day of the month. There are fifteen possible values:
    Blank = No source (e.g., data value missing)
    0 = U.S. Cooperative Summary of the Day (NCDC DSI-3200)
    6 = CDMP Cooperative Summary of the Day (NCDC DSI-3206)
    7 = U.S. Cooperative Summary of the Day -- Transmitted via WxCoder3 (NCDC DSI-3207)
    A = U.S. Automated Surface Observing System (ASOS) real-time data (since January 1, 2006)
    B = U.S. ASOS data for October 2000-December 2005 (NCDC DSI-3211)
    F = U.S. Fort Data
    G = Official Global Climate Observing System (GCOS) or other government-supplied data
    H = High Plains Regional Climate Center real-time data
    M = Monthly METAR Extract (additional ASOS data)
    N = Community Collaborative Rain, Hail, and Snow (CoCoRaHS)
    R = NCDC Reference Network Database (Climate Reference Network and Historical Climatology Network-Modernized)
    S = Global Summary of the Day (NCDC DSI-9618)
 
NOTE: "S" values are derived from hourly synoptic reports exchanged on the Global Telecommunications System (GTS). Daily values derived in this fashion may differ significantly from "true" daily data, particularly for precipitation (i.e., use with caution).
    T = SNOwpack TELemtry (SNOTEL) data obtained from the Western Regional Climate Center
    U = Remote Automatic Weather Station (RAWS) data obtained from the Western Regional Climate Center
    W = WBAN/ASOS Summary of the Day from NCDC's Integrated Surface Data (ISD)
    X = U.S. First-Order Summary of the Day (NCDC DSI-3210)
    Z = Datzilla official additions or replacements
VALUE2   is the value on the second day of the month.
MFLAG2   is the measurement flag for the second day of the month.
QFLAG2   is the quality flag for the second day of the month.
SFLAG2   is the source flag for the second day of the month.
 
...and so on through the 31st day of the month. Note: if the month has less than 31 days, then the remaining variables are set to missing (e.g., for April, VALUE31 = -9999, MFLAG31 = blank, QFLAG31 = blank, SFLAG31 = blank).

Data Access

The USHCN Daily data are available via FTP or a Web interface that allows users to query, plot, and download data for individual states, stations, and variables. Please see the USHCN Data Access page.

References

  • Easterling, D. R., T. R. Karl, E. H. Mason, P. Y. Hughes, and D. P. Bowman. 1996. United States Historical Climatology Network (U.S. HCN) Monthly Temperature and Precipitation Data. ORNL/CDIAC-87, NDP-019/R3. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 280 pp.
  • Hughes, P. Y., E. H. Mason, T. R. Karl, and W. A. Brower. 1992. United States Historical Climatology Network Daily Temperature and Precipitation Data. ORNL/CDIAC-50, NDP-042. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 140 pp.
  • Karl, T. R., C. N. Williams, Jr., and F. T. Quinlan. 1990. United States Historical Climatology Network (HCN) Serial Temperature and Precipitation Data. ORNL/CDIAC- 30, NDP-019/R1. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
  • Quinlan, F. T., T. R. Karl, and C. N. Williams, Jr. 1987. United States Historical Climatology Network (HCN) serial temperature and precipitation data. NDP-019. Carbon Dioxide Information Analysis Center. Oak Ridge National Laboratory, Oak Ridge, Tennessee.
  • Williams, C. N., R. S. Vose, D. R. Easterling, and M. J. Menne, 2004. United States Historical Climatology Network Daily Temperature, Precipitation, and Snow Data. ORNL/CDIAC-118, NDP-070. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Contacts

Questions regarding the USHCN Daily web site or data may be directed to Dale Kaiser at CDIAC.


Please cite data as: M. J. Menne, C. N. Williams, Jr., and R. S. Vose, 2013. United States Historical Climatology Network Daily Temperature, Precipitation, and Snow Data. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.