Jeff, The GEMPAK convention is P--M, where the prcipitation will be in millimeters (or equivalently in unit volume). The "--" in the above is used to specify the time period of accumulation. That is, a 6 hourly accumulation would be P06M. You will find the model spcifications of units and parameters in the tables under $GEMTBL/grid/. The period of accumulation is typically important since the model outputs may have to be subtracted from interving times (eg P03M at F009 and P06M at F012, GEMPAK will compute P03M at F012 using the appropriate subtraction. Steve Chiswell Unidata User Support Ticket Details =================== Ticket ID: OLD-938565 Department: Support GEMPAK Priority: Normal Status: Closed