considered normal, and a value greater than 75 is considered above normal. Only stations with at least 30 years of record are used. For the example shown, there appears to be drought conditions along the east coast of the United States. The NWIS Automated Data Processing System (ADAPS) contains more than 850,000 station years of time-series data that describe stream-water levels, stream flow (discharge), reservoir water levels, surface-water quality, groundwater levels, and rainfall. ADAPS consists of a collection of computer programs and databases. The water data stored in ADAPS result from the processing of data collected by automated recorders and by observations and manual measurements at field installations around the nation. The data from these sites are transported by field personnel or are relayed through telephones or satellites to offices where USGS personnel, using ADAPS proce- dures, process the data. The data relayed through the Geostationary Operational Environmental Satellite (GOES) system are processed automatically in near-real time, and in many cases are avail- able within minutes on the USGS Web pages.
11.3.5 prisM PRISM (Parameter-elevation Regressions on Independent Slopes Model) is an expert system that uses point data and a digital elevation model (DEM) to generate gridded estimates of climate parameters (Daly et al 1994; http://www.prism.oregonstate.edu/). Although PRISM was originally developed for precipitation mapping, it was quickly recognized that the model philosophy, i.e., that the topographic facet is an important climatic unit and that elevation is a primary driver of climate patterns, could be extended to other climate parameters. PRISM has since been used to map temperature, snowfall, weather generator statistics, and others. PRISM was developed to overcome the deficiencies of stan- dard spatial interpolation methods, where orographic effects strongly influence weather patterns. In operation, PRISM gives the user the option to use the DEM to estimate the elevations of pre- cipitation stations at the proper orographic scale, and to use the DEM and a windowing technique to group stations onto individual topographic facets. For each DEM grid cell, PRISM develops a weighted precipitation/elevation (P/E) regression function from nearby stations, and predicts pre- cipitation at the cell’s DEM elevation with this function. In the regression, greater weight is given to stations with locations, elevations, and topographic positionings similar to that of the grid cell. Whenever possible, PRISM calculates a prediction interval for the estimate, which is an approxima- tion of the uncertainty involved.