From US’s National Weather Service – big precipitation anomalies in US this past year. The purple areas are extra wet, while the red areas are extra dry.
“Normal” precipitation is derived from PRISM climate data, created at Oregon State University. The PRISM gridded climate maps are considered the most detailed, highest-quality spatial climate datasets currently available. The 30 year PRISM normal from 1971-2000 is used for precipitation analysis since 2004. Prior to 2004 the 30 year PRISM normal from 1961-1990 is used.” from http://water.weather.gov/precip/about.php