GCIP LSA-NW EAOP 2000 Daily Precipitation Composite 1.0 General Description The GCIP LSA-NW EAOP 2000 Daily Precipitation Composite 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) 2000. This precipitation composite is composed of data from several sources (i.e., National Centers for Environmental Prediction/ Climate Prediction Center (NCEP/CPC) daily precipitation data, National Weather Service (NWS) Cooperative Observers (COOP) daily precipitation data, North Dakota Atmospheric Resource Board (NDARB) daily precipitation data, Natural Resource Conservation Service (NRCS) National Water and Climate Center SNOwpack TELemetry (SNOTEL) daily precipitation data, and the daily precipitation data extracted from the GCIP LSA-NW EAOP-00 Hourly Precipitation Composite). Data from these sources were quality controlled and merged to form this precipitation composite. This composite contains data for the GCIP LSA-NW EAOP-00 domain and time period (01 April 2000 through 31 March 2001). The GCIP LSA-NW EAOP-00 domain is approximately 90W to 115W longitude and 36N to 51N latitude. 2.0 Detailed Data Description 2.0.1 NCEP/CPC Daily Precipitation Algorithms The Climate Prediction Center (CPC) is a component of the National Centers for Environmental Prediction (NCEP). 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. 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-00 Daily Precipitation Composite. 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. Data from cooperators networks such as NCEP/CPC has hundreds of reporting locations change from incremental to accumulator and back to incremental. Others, especially NCEP/CPC stations in West Virgina and Western portions of Pennsylvania changed a couple of times and have now settled on accumulators. Anyone using this data must be aware of the dynamic changes in the network of sites that are processed by HADS...and be aware of the potential lag time from when a change is implemted to when we become aware of the change. This is far, far from a stable environment. To help users in identifying these changes, 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. 2.0.2 NWS Cooperative Observer (COOP) Daily Precipitation Algorithms 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. Only incremental values are included in the GCIP LSA-NW EAOP-00 Daily Precipitation Composite. For more information, see NCDC, 1991. 2.0.3 North Dakota Atmospheric Resource Board (NDARB) Daily Precipitation Algorithms The NDARB rain gauges are all the same in each observer site. They are Tru-Chek "wedge type" rain gauges, which are issued from the NDARB office in Bismarck, ND. The only variable in siting is the individual siting of each gauge. NDARB relies on the volunteers to follow directions and site them properly. NDARB observers are asked take daily readings as near to 8AM as possible each day. The NDARB network only collects data from April through September each year. These data are provisional. The algorithms used to compute the NDARB daily precipitation data are not currently available. The NDARB web site can be found at http://www.swc.state.nd.us/. 2.0.4 Natural Resource Conservation Service (NRCS) National Water and Climate Center SNOwpack TELemetry (SNOTEL) Daily Precipitation Algorithms Introduction The Natural Resources Conservation Service (NRCS) installs, operates, and maintains an extensive, automated system to collect snowpack and related climatic data in the Western United States called SNOTEL (for SNOwpack TELemetry). The system evolved from NRCS's Congressional mandate in the mid-1930's "to measure snowpack in the mountains of the West and forecast the water supply." The programs began with manual measurements of snow courses; since 1980, SNOTEL has reliably and efficiently collected the data needed to produce water supply forecasts and to support the resource management activities of NRCS and others. Climate studies, air and water quality investigations, and resource management concerns are all served by the modern SNOTEL network. The high-elevation watershed locations and the broad coverage of the network provide important data collection opportunities to researchers, water managers, and emergency managers for natural disasters such as floods. Meteor Burst Technology SNOTEL uses meteor burst communications technology to collect and communicate data in near-real-time. VHF radio signals are reflected at a steep angle off the ever present band of ionized meteorites existing from about 50 to 75 miles above the earth. Satellites are not involved; NRCS operates and control the entire system. An available map shows the locations of over 600 SNOTEL sites in 11 western states including Alaska. The sites are generally located in remote high-mountain watersheds where access is often difficult or restricted. Access for maintenance by NRCS includes various modes from hiking and skiing to helicopters. Sites are designed to operate unattended and without maintenance for a year. They are battery powered with solar cell recharge. The condition of each site is monitored daily when it reports on 8 operational functions. Serious problems or deteriorating performance trigger a response from the NRCS electronic technicians located in 6 Data Collection Offices. The SNOTEL sites are polled by 2 master stations operated by NRCS in Boise, Idaho, and Ogden, Utah. A central computer at NRCS's National Water and Climate Center (NWCC) in Portland, Oregon controls system operations and receives the data collected by the SNOTEL network. New SNOTEL System Capabilities Basic SNOTEL sites have a pressure sensing snow pillow, storage precipitation gage, and air temperature sensor. However, they can accommodate 64 channels of data and will accept analog, parallel, or serial digital sensors. On-site microprocessors provide functions such as computing daily maximum, minimum, and average temperature information. Generally, sensor data is recorded every 15 minutes and reported out in a daily poll of all sites. Special polls are conducted more frequently in response to specific needs. The new generation of remote sites, master stations, and central computer facilities allows for hourly interrogation of remote sites. The system has the ability to vary the configuration of a remote site by transmitting the appropriate commands telling the remote site what sensors to turn on or what parameters to send. A variety of calculations can be made on any sensor channel. For example, the user can select maximum, minimum, average, standard deviation, or circular averaging. Each sensor can be accessed independently at a specific interval. For example, wind speed may be sensed every minute during the day to arrive at an average, while the snow pillow may be accessed every 15 minutes for the accumulated total. System performance has increased over the years, mainly due to a better understanding of meteor burst communication characteristics and improved equipment. While a 95 percent response to a system- wide poll is the standard, over 99 percent is common. Data Storage, Management and Accessibility All data are received by the SNOTEL central computer, which in turn is linked to the Centralized Forecasting System (CFS) in the NWCC where data can be accessed. Once on CFS, the data are in a relational database, where various analysis and graphics programs are available. Current and historical data and analyses are available by dialing in to the CFS, by disk or tape media, paper copy, or more recently via NWCC homepage and internet. While carrying out the agency mission is paramount, NRCS is interested in supporting the research and operational data collection needs of others. The current system offers excellent opportunities. For more information, see the SNOTEL web pages at: http://www.wcc.nrcs.usda.gov/snotel http://www.wa.nrcs.usda.gov/snow/index.htm http://www.civil.utah.edu/~cv5450/snotel/standards.htm SNOTEL data is provisional and subject to revision. The following parameter was converted to JOSS QCF format when it existed in the raw data: Prec - "Accumulated Precip Since", in inches x 100 was converted to QC format incremental precipitation in mm. The accumlation period was reset on Oct 1 of each year. No other parameters were converted. 2.0.5 Daily Precipitation Extracted from GCIP LSA-NW EAOP 2000 Hourly Precipitation Composite Each daily precipitation incremental value in this dataset was formed by summing the 24 hourly precipitation values extracted from each GCIP LSA-NW EAOP-00 Hourly Precipitation Composite record. The hourly values are summed from hour 0100 through hour 2400 (0000 UTC next day). The value reported for any daily observation represents data collected during the previous 24 hours. An error was discovered in the LDMSFCMETR processing. Due to a coding error, the record for the last hour of the last day a LDMSFCMETR station reported during the GCIP LSA_NW EAOP 2000 time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire GCIP LSA_NW EAOP 2000 time of interest, most of these missing records occur on Mar 31, 2000. A total of 392 records were deleted (one for each LDMSFCMETR station). This bug affects the GCIP LSA_NW EAOP 2000 hourly surface nominals composite (but NOT the GCIP LSA_NW EAOP 2000 surface specials composite), and thus the GCIP LSA_NW EAOP 2000 hourly and daily precip composites as well. 2.1 Detailed Format Description The Daily Precipitation Composite 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. 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". An error was discovered in the LDMSFCMETR processing. Due to a coding error, the record for the last hour of the last day a LDMSFCMETR station reported during the GCIP LSA_NW EAOP 2000 time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire GCIP LSA_NW EAOP 2000 time of interest, most of these missing records occur on Mar 31, 2000. A total of 392 records were deleted (one for each LDMSFCMETR station). This bug affects the GCIP LSA_NW EAOP 2000 hourly surface nominals composite (but NOT the GCIP LSA_NW EAOP 2000 surface specials composite), and thus the GCIP LSA_NW EAOP 2000 hourly and daily precip composites as well. 2.1 Detailed Format Description 3.0 Quality Control Processing This precipitation composite is composed of data from several sources (i.e., National Centers for Environmental Prediction/ Climate Prediction Center (NCEP/CPC) daily precipitation data, National Weather Service (NWS) Cooperative Observers (COOP) daily precipitation data, North Dakota Atmospheric Resource Board (NDARB) daily precipitation data, Natural Resource Conservation Service (NRCS) National Water and Climate Center SNOwpack TELemetry (SNOTEL) daily precipitation data, and the daily precipitation data extracted from the GCIP LSA-NW EAOP-00 Hourly Precipitation Composite). Each of these datasets was independently Quality Controlled. 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. 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. After the datasets were merged to form the GCIP LSA-NW EAOP-00 Daily Precipitation Composite, a statistics program was executed to ensure that the quality of the individual datasets had been retained. 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, 25 pp. Natural Resources Conservation Sevice, National Water and Climate Center, Snowpack Telemetry (SNOTEL) Data Network, Accessed October 2002 [Available online from http://www.wcc.nrcs.usda.gov/snotel] North Dakota State Water Commission Home Page, accessed October 2002 [Available online from http://www.swc.state.nd.us/]