Description:
The percentiles shown indicate a ranking of  precipitation anomalies (for the month shown on plot) with the 0th percentile being the driest on record and the 100th percentile (shown as 1 on the plot) being the wettest.  Green and dark green shading is above 80th and 90th percentile, respectively; regions shaded in light and dark brown indicate precipitation below the 20th and 10th percentile, respectively. Regions with grey shading receive less than 10 mm of precipiation for the month displayed on plot.

The precipitation data is based on satellite  estimates over ocean areas and rain guage data over land regions.  The period used for computing the percentiles is 1961-1990.  "CAMS" is an acronym for the "Climate Anomaly Monitoring System" in use at the Climate Prediction Center (CPC) at the US National Centers for Environmental Prediction (NCEP).  "OPI" stands for "Outgoing longwave radiation Precipitation Index" (the satellite precipitation estimates are based on emitted longwave radiation observed by polar-orbiting satellite.)