Climate and Weather Resources
National Weather Service GIS Data Portal
"Many of the National Weather Service data sets are available in formats that are able to be imported directly into Geographic Information Systems (GIS). Data formats include downloadable shapefiles, web services and even KML files." Also part of NOAA.
NOAA's National Climatic Data Center
The largest archive of weather data. The GIS Map Services Index provides access to the data and the interactive map application displays available data.
PRISM Climate Group's Climate Data
Spatial climate data sets developed by the PRISM climate mapping program at Oregon State University's Spatial Climate Analysis Service (SCAS). Download compressed ASCII files that can be converted to rasters.