use hrrr surface temp, wind. other refactoring

[wholmgren]

• Closes HRRR weathermodel 'temp_air' calculation wrong #604
• I am familiar with the contributing guidelines.
• Fully tested. Added and/or modified tests to ensure correct behavior for all reasonable inputs. Tests (usually) must pass on the TravisCI and Appveyor testing services.
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate docs/sphinx/source/whatsnew file for all changes.
• Code quality and style is sufficient. Passes LGTM and SticklerCI checks.
• New code is fully documented. Includes sphinx/numpydoc compliant docstrings and comments in the code where necessary.
• Pull request is nearly complete and ready for detailed review.

[wholmgren]

Tests pass. I suggest that we not worry about the untested line that handles and exception. If it works, great, we get a more informative message. If it fails, well, it was going to fail anyways.

I'll merge soon unless I hear objections or a review comes in. Keep in mind that a lot this code might change in the next 6 months.

[cwhanse]

LGTM