| Flag | Definition |
|---|---|
| A | Data as received from NCDC, converted to SI units |
| B | Linearly interpolated |
| C | Non-linearly interpolated to fill data gaps
from 6 to 47 hours in length |
| D | Not used |
| E | Modeled or estimated, except: precipitable water,
calculated from radiosonde data; dew point temperature calculated from dry bulb temperature and relative humidity; and relative humidity calculated from dry bulb temperature and dew point temperature |
| F | Precipitable water, calculated from surface
vapor pressure; aerosol optical depth, estimated from geographic correlation |
| ? | Source does not fit any of the above. Used mostly for missing data |