utc2nwislocal, UTC date-times to NWIS local time zones using UTC offsets

The utc2nwislocal package in the R language provides a light-weight, dependency-free utility for converting Coordinated Universal Time (UTC) base::as.POSIXct() date-time values into character-string representations for time zones. The UTC offsets for individual time zones are determined from the time-zone codes recognized by the U.S. Geological Survey National Water Information System (NWIS) database. The time zones are tracked in a separate database slot than the UTC date time. Sometimes it can be difficult in the R language to work with its Olson time-zone naming convention (base:OlsonNames()) relative to the time zone codes of NWIS. This package could help users working with some NWIS-derived data sets.