Watershed Data Management (WDM) database file ARGN21.WDM is an update of ARGN20.WDM (Bera, 2021) with the processed data from October 1, 2020 through September 30, 2021, appended to it. The primary data were downloaded from the Argonne National Laboratory (ANL) (Argonne National Laboratory, 2022) and processed following the guidelines documented in Over and others (2010). ARGN21.WDM file contains nine data series: air temperature, in degrees Fahrenheit (dsn 400), dewpoint temperature, in degrees Fahrenheit (dsn 500), wind speed, in miles per hour (dsn 300), solar radiation, in Langleys (dsn 600), computed potential evapotranspiration, in thousandths of an inch (dsn 200), and four data-source flag series for air temperature (dsn 410), dewpoint temperature (dsn 510), wind speed (dsn 310), and solar radiation (dsn 610), respectively, from January 1,1948, to September 30, 2021. Daily potential evapotranspiration (PET) were computed from average daily air temperature, average daily dewpoint temperature, daily total wind speed, and daily total solar radiation and disaggregated to hourly PET, in thousandths of an inch, using the Fortran program LXPET (Murphy, 2005). Missing and apparently erroneous data values were replaced with adjusted values from nearby weather stations used as "backup." The Illinois Climate Network (Water and Atmospheric Resources Monitoring Program, 2022) station at St. Charles, Illinois, was used as "backup" for the hourly air temperature, solar radiation, and wind speed data. The Midwestern Regional Climate Center (Midwestern Regional Climate Center, 2022) provided the hourly dewpoint temperature and wind speed data collected by the National Weather Service from the station at O'Hare International Airport and used as "backup." Each data source flag is of the form "xyz", which allows the user to determine its source and the methods used to process the data (Over and others, 2010). To open this file user needs to install the utility described in the section "Related External Resources" on this page. References Cited: Argonne National Laboratory, 2022, Meteorological data, accessed on January 17, 2022, at https://www.atmos.anl.gov/ANLMET/numeric/. Bera, M., 2021, Meteorological Database, Argonne National Laboratory, Illinois, January 1, 1948 - September 30, 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9GP8COF. Midwestern Regional Climate Center, 2022, Meteorological data, accessed on March 2, 2022, at https://mrcc.purdue.edu/CLIMATE/. Murphy, E.A., 2005, Comparison of potential evapotranspiration calculated by the LXPET (Lamoreux Potential Evapotranspiration) Program and by the WDMUtil (Watershed Data Management Utility) Program: U.S. Geological Survey Open-File Report 2005-1020, 20 p., https://pubs.er.usgs.gov/publication/ofr20051020. Over, T.M., Price, T.H., and Ishii, A.L., 2010, Development and analysis of a meteorological database, Argonne National Laboratory, Illinois: U.S. Geological Survey Open-File Report 2010-1220, 67 p., http://pubs.usgs.gov/of/2010/1220/. Water and Atmospheric Resources Monitoring Program. Illinois Climate Network, 2022. Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. Data accessed on January 4, 2022, at http://dx.doi.org/10.13012/J8MW2F2Q.