The NEX-DCP30 data set statistically downscales general circulation models with varying grid resolutions to 30 arc seconds (~800m). The consistent grid spacing and fine resolution makes creating county averages simple.
Step 1) A GIS shapefile for the continental United States counties is used to assign each 30 arc second grid cell a county ID for all the cells within the county boundaries. The example above shows counties within Oregon, but the method is applied to all continental United States counties.
Step 2) Anomalies for temperature and precipitation are calculated for the periods 2025-2049, 2050-2074 and 2075-2099 against the base period of 1980-2004. The 30 arc second anomalies are displayed in the application maps.
Step 3) The county ID mask created in Step 1 is used to calculate area weighted averages of the anomalies for every county for each month between 1980-2099. The county averages are used in the application climographs, histograms, time series and data tables.