Replace single-character variables in schema with more descriptive names

[WalterKolczynski-NOAA]

Description schema.py uses single-character variables in places when more descriptive variables names would be better.

Requirements Variable names should be descriptive enough to know what they are without seeing the declaration. Single-character names are especially problematic because they are also difficult to search for.

Acceptance Criteria (Definition of Done) All vague variable names replaced with more descriptive names.

Dependencies None

[aerorahul]

@WalterKolczynski-NOAA schema.py has been fork-lifted for convenience and we have tried to keep it as close as possible to the original (exception fixing pycodestyle errors) to allow easy updates if/when the code needs to be synced with upstream.