Standardized Precipitation Index Map Selector

Map Date: January February March April May June July August September October November December 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Calculate mean and standard deviation
Use stored mean and standard deviation (if available)