Yes, I'd like a facility to enter a date and an observed precipitation amount, which will override the local weather station data for that day.
We frequently get scattered thunderstorms that can drop 0.5" at the airport weather station, but nothing in my yard, so I'd want to input an override of 0.0" for that date so my Iro doesn't think my soil has more moisture than it does. There can be other times the airport gets 0.1" while I have a downpour giving me 0.75".
A good interface would take the user to a table, listing dates and observed rainfall at the chosen weather station (this data is currently feeding the program's calculation for available water per zone). That table would have a third column that a user can click into and enter an override value per date. If there is no override present for a date, the system uses the weather station data.
In the current system, the only way I can change the moisture level for a zone is to use the "club" of clicking Fill or Empty. Having an override input interface would give me "arrows" to give more precision to the system.