82 warnings are currently issued in the process of running our test suite:
https://gist.github.com/shoyer/db0b2c82efd76b254453216e957c4345

Some of can probably be safely ignored, but others are likely noticed by users, e.g.,
https://stackoverflow.com/questions/41130138/why-is-invalid-value-encountered-in-greater-warning-thrown-in-python-xarray-fo/41147570#41147570

It would be nice to clean up all of these, either by catching the appropriate upstream warning (if irrelevant) or changing our usage to avoid the warning. There may very well be a lurking FutureWarning in there somewhere that could cause issues when another library updates.

Probably the easiest way to get started here is to get the test suite running locally, and use py.test -W error to turn all warnings into errors.