It’s almost certainly the choice of units, either for display or in the log files. Under Customize, find the precipitation units in BOTH “units for display here” AND in “units in WD or Cumulus log files”. I think you want them in millimeters (?). By the way, if you are using km/hr as units for display, you should choose KNOTS (I know, strange but true!) for the units in log files.
Let me know if that takes care of it!
Tom