Hi @ndr-oftheline and @paul121 - there is a farmOS Weather module (optional add-on) available at https://github.com/farmOS/farm_weather which could serve as a starting point for this.
Currently, the module provides a “Quick Form” for recording precipitation events as observations (essentially what @paul121 described).
@jgaehring is actually in the process of thinking through converting that to a “Field Module” in farmOS Field Kit, so that it can be used in the offline/mobile app.
A next step would be to build a report in the farmOS UI that summarizes/visualizes the observations that it collects, like @ndr-oftheline described. That would be great! @paul121 recently built an animal weight report that could be used as an example (and perhaps some of the logic or UI could be generalized/shared between them).
The one thing that the Weather module’s observations do NOT collect yet is location. It just asks for total precipitation, whether it is rain/snow, and has a field for notes. We could potentially just add an area reference field as well, so that you can reference the specific area/location where the measurement was taken. This would be useful for farms that have many fields spread out over a larger area.