new "Explorer" tab

[gassc]

Create a new context/view that is:

• unifies the workflow for provisional and qa/qc'd data; a "best of"
• puts the rainfall events front-and-center
• emphasizes visualization of stats between sensors and over time
• enables comparison and diffing between different events.
• by default has no geographic constraints: all gauges, all pixels

This would use a lot of the existing and planned components under the hood, but re-arrange them to support a new, exploratory workflow.

This could also possibly be done (or at least prototyped) in a Dash app.