Precipitation Monthly Normal for 1981-2010 from Daymet

This raster dataset shows the monthly normal precipitation (rain plus melted snow) in millimeters with a grid cell resolution of 1000-meters (1-kilometer). The normal is defined as the arithmetic mean of the annual sum of daily precipitation over a 30-year period. The current 30-year interval for calculating normals is 1980 to 2010. The standard deviation is also provided for calculating daily or annual z-score departures or similar statistics. Normals serve as a reference point for comparing current climatological trends to that of the past. A 30-year period is long enough to filter out any inter-annual variation or anomalies, but sufficiently short enough to reflect longer term climatic trends. The 30-year interval was selected by international agreement, based on the recommendations of the International Meteorological Conference in Warsaw in 1933.