Use preset colorbar levels fort at least one variable

[jfrost-mo]

What problem does your feature request solve?

Currently we have support for defined levels, but no way to test it as no variables use it.

Describe the solution you'd like

A variable to use it. It was discussed that precipitation rate would be a good candidate, as that has pre-set non-uniform bins as a PWS metric.

Describe alternatives you've considered

If nothing actually uses set levels we should remove support for them.