Which of the following would indicate that specific values were not obtained in a METAR report?

In the context of METAR reports, the indication that specific values were not obtained is represented by "NA," which stands for "Not Applicable." This term is used when certain pieces of information are not relevant or were not available at the time of reporting.

The other terms have different meanings: "VA" indicates volcanic ash, which is an event rather than an indication of missing data. "UN" denotes "unknown," implying that the data is not known, but it does not specifically address the absence of collected values. "NG" refers to "No Gusts," which indicates the absence of wind gusts; while this is a form of reporting missing data regarding wind conditions, it is not a general indication of all missing values.

Therefore, "NA" is the correct representation for situations where specific data points are not applicable or available in a METAR report.