GCIP LSA-NW EAOP 1999 NCEP/CPC Daily Precipitation Data in QC format 1.0 General Description The National Centers for Environmental Prediction/ Climate Prediction Center (NCEP/CPC) daily precipitation data in QC format is one of several precipitation datasets provided in the GEWEX Continental-Scale International Project (GCIP) Large Scale Area-North West (LSA-NW) Enhanced Annual Observing Period (EAOP) 1999. Data from this source was quality controlled. This dataset contains data for the GCIP LSA-NW EAOP-99 domain and time period (01 April 1999 through 31 March 2000). The GCIP LSA-NW EAOP-99 domain is approximately 90W to 115W longitude and 36N to 51N latitude. 2.0 Detailed Data Description NCEP/CPC Daily Precipitation Algorithms The NCEP/CPC daily precipitation dataset was formed by extracting data with NCEP/CPC element codes of PC and PP that fall on the hour. All raw precipitation data, including data that do not fall on the hour, can be found on codiac in the GCIP/EOP Surface: Precipitation NCEP/CPC Gage Only Daily Dataset. The NCEP/CPC observations of daily precipitation can include multiple measurements for a given day. When this occurs, the precipitation for that day is set to missing in the UCAR/JOSS GCIP LSA-NW EAOP-99 Daily Precipitation Data. The value reported for any daily observation represents data collected during the previous 24 hours. NCEP/CPC excludes any precipitation value greater than 20 inches from the NCEP/CPC daily precipitation dataset. The information above was gathered from personal correspondence with NCEP/CPC during 1997 and 1998. UCAR/JOSS checks the NCEP/CPC daily precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the NCEP/CPC network to "questionable". For this purpose, UCAR/JOSS defines accumulated precipitation to be six identical, sequential daily precipitation values potentially followed by additional identical values or values that increase over time. 2.1 Detailed Format Description The NCEP/CPC GCIP LSA-NW EAOP-99 Daily Precipitation Data 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. UCAR/JOSS also checks the NCEP/CPC daily precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the NCEP/CPC network to "questionable". 3.0 Quality Control Processing Gross limit checks were used to determine the quality of the data in this dataset. 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. UCAR/JOSS also checks the CPC/NCEP daily precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the CPC/NCEP network to "questionable". For this purpose, UCAR/JOSS defines accumulated precipitation to be six identical, sequential daily precipitation values potentially followed by additional identical values or values that increase over time. 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 and 2 list the quality control flags and codes plus their meanings. 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 None.