As Steve (and Dongxiao Zhang) suggested, here was my solution: !.... define axis/t="01-JAN-1000":"31-DEC-1299":30.4375/unit=days monax ! use dataset.nc ! let/title="Monthly Average Var" var_new = var[gt=monax@ave] save/file=dataset_m.nc var_new !.... Works like a charm! Thanks! -- Gary Strand strandwg@ucar.edu http://www.cgd.ucar.edu/ccr/gary