2011 precipitation anomalies in USA

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.

Precipitation anomalies in USA for 2011 in mm

update:

“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

2 thoughts on “2011 precipitation anomalies in USA”

  1. Extra wet and extra dry? Compared to what? HOw is “normal” precipitation determined for this purpose?

  2. Its explained via the link to the figure source

    http://water.weather.gov/precip/about.php

    “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.”

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