Update snow events parameter docs for Townsend snow loss model

[aturabi]

• Closes Update documentation for snow events parameter for Townsend snow loss model #1839
• I am familiar with the contributing guidelines
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

[cwhanse]

thanks @aturabi !

[cwhanse]

@kandersolar there are unrelated test failures. Weird.

[kandersolar]

@kandersolar there are unrelated test failures. Weird.

I suspect scipy/scipy#19103 is to blame, although I did not investigate locally.

[kandersolar]

Perhaps we should add a sentence to the second paragraph of the Notes section saying "The 1 inch threshold for snow events documented above is also based on private communication with the model's author.", or similar?

[kandersolar]

Thanks @aturabi!