NCDC Summary of the Day Co-operative Daily Precipitation Data 1.0 General Description The National Climatic Data Center (NCDC) Summary of the Day Co-operative Precipitation Dataset is one of several surface precipitation datasets provided in the GEWEX Continental-Scale International Project (GCIP) by UCAR/JOSS. 2.0 Detailed Data Description The observations in this dataset are primarily those from the cooperative network, augmented by observations from principal observing stations operated by the National Weather Service (NWS) and other sites having highly trained observers. The primary thrust of the cooperative observing program today is the recording of 24-hour precipitation amounts. The observations are for the 24-hr period ending at the time of observation. Observer convenience or special program needs mean that observing times vary from station to station. However, the vast majority of observations are taken near either 7:00 AM or 7:00 PM local time. Details of procedures and recording practices of the observers are documented in the "National Weather Service Observing Handbook No. 2". 2.0.1 Precipitation Data The NWS Cooperative Observer Daily Precipitation dataset was formed by extracting the daily incremental precipitation values provided in the National Climatic Data Center (NCDC) TD 3200 dataset. The incremental value reported for any daily observation represents data collected during the previous 24 hours. 2.1 Detailed Format Description The Daily Precipitation data set contains six metadata parameters and four data parameters. The metadata parameters describe the station location and time at which the data were collected. The four data parameters repeat once for each day in the monthly record. Every record has 31 days reported, regardless of the actual number of days in the month. For months with less than 31 days, the extra days are reported as missing (i.e., '-999.99 7 M'). Each 24 hour precipitation value has an associated observation hour. The observation hour is the ending UTC hour for the 24 hour period for which the precipitation value is valid. Data values are valid for the 24 hours preceding the observation hour given for the day. A Quality Flag and a Quality Control (QC) Code are assigned to each data value during quality control processing. For a list of possible Quality Flag and QC Code values see the Quality Control section 3.0. The table below details each parameter. Parameters Units ---------------------- ------------------------------------- Date of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network Dependent Latitude Decimal degrees, South is negative Longitude Decimal degrees, West is negative Station Occurrence Unitless Daily Precip Value millimeters Quality Flag See list of Definitions QC Code See list of Definitions Observation hour Beginning UTC hour for 24 hour period for which value is valid. 2.2 Data Remarks Negative precipitation and values too large to be represented in the output format were changed to missing ('-999.99') and were assigned the 'C' QC code. The NCDC Summary of Day Co-operative data have observation hours that vary by station. Data values are valid for the 24 hours preceding the observation hour given for the day. 3.0 Quality Control Processing Gross limit checks were used to determine the quality of the data in this composite. Data values less than 101.6 millimeters (4 inches) were flagged as good. Any data value greater than or equal to 101.6 millimeters but less than 127 millimeters (5 inches) was flagged as questionable. Any data value greater than or equal to 127 millimeters was flagged as unlikely. Several questionable and unlikely data values were also manually inspected. After inspection, the quality control code and flag may have been manually updated to better reflect the likelihood of the actual occurrence of the precipitation value based on an isohyet analysis. Data were never modified, unless the precipitation value was negative or too large to be represented in the output format. In these cases the data value was flagged with a QC code of 'C' and changed to a missing value (i.e., '-999.99'). Table 1 Quality Control Flag Description --------------------------- --------------------------------------------- 0 No qualifier required 1 Accumulation period 2 End of Accumulation period 3 Deleted value. Original data was unreadable. 4 Trace of precipitation. 5 Probable amount as a result of melting frozen precipitation. 6 Suspect amount relative to time or period of occurrence. 7 Missing value Table 2 QC Code Description ----------------- ------------------------------------------ U Unchecked G Good M Normally recorded but missing D Questionable B Unlikely N Not available or Not observed. X Glitch E Estimated C Reported value exceeds output format field size or was negative precipitation. T Trace I Derived parameter can not be computed due to insufficient data. 4.0 References National Climatic Data Center, 1991: Surface Land Daily Cooperative; Summary of the Day TD-3200. National Climatic Data Center, Asheville, NC, 25pp. NOAA, National Weather Service, 1989: National Weather Service Observing Handbook No. 2, Cooperative Station Observations. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Silver Spring, MD. 83 pp.