The Areal edited (raw) data is the original (or raw) data that have been screened to flag monthly data that are suspect/outliers (over 3 standard deviations from period of record mean of the element). Note that the outliers are only flagged: they are still present in the data.
The Time of Observation data (tos) is the Areal Edited data that have been adjusted to remove the time of observation bias so that the data will be consistent with a midnight-to-midnight observation schedule.
The Filnet data (filnet) is the Time of Observation data that have been adjusted for the Maximum/Minimum Temperature System (MMTS) bias, station moves/changes bias, and contains estimated values for missing/outlier data.
The Urban Adjusted data (urban) is the Filnet data that have been adjusted for bias due to urbanization effects.
The Confidence factor data (cfv) is a measure of data quality.
See NCDC's documentation for more information. Also see the detailed documentation.
Karl, T.R., C.N. Williams, Jr., P.J. Young, and W.M. Wendland, 1986: A model to estimate the time of observation bias associated with monthly mean maximum, minimum, and mean temperature for the United States, J. Climate Appl. Meteor., 25, 145-160.
Karl, T.R., and C.W. Williams, Jr., 1987: An approach to adjusting climatological time series for discontinuous inhomogeneities, J. Climate Appl. Meteor., 26, 1744-1763. Karl, T.R., H.F. Diaz, and G. Kukla, 1988: Urbanization: its detection and effect in the United States climate record, J. Climate, 1, 1099-1123.
Karl, T.R., C.N. Williams, Jr., F.T. Quinlan, and T.A. Boden, 1990: United States Historical Climatology Network (HCN) Serial Temperature and Precipitation Data, Environmental Science Division, Publication No. 3404, Carbon Dioxide Information and Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 389 pp.