Flight Rules Conditions
https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table4-2-3-3.shtml
PBMVFRC
Probability of Encountering Marginal Visual Flight Rules Conditions
%
PBLIFRC
Probability of Encountering Low Instrument Flight Rules Conditions
%
PBINFRC
Probability of Encountering Instrument Flight Rules Conditions
%