# MADIS QC flags

> The six data descriptors MADIS attaches to every observation, from Z through X, and which ones forecasters can use.

Weather stations · Reference · https://wxalerts.org/docs/weather-stations/madis-qc-flags/

Every observation carries a data descriptor, which is how you find out whether anyone is actually using your data.

| Flag | Meaning |
| --- | --- |
| **Z** | Preliminary, no QC applied |
| **C** | Coarse: passed level 1 validity |
| **S** | Screened: passed levels 1 and 2 (internal, temporal, statistical-spatial consistency) |
| **V** | Verified: passed levels 1 through 3, including spatial consistency |
| **Q** | Questioned: passed level 1, failed 2 or 3 |
| **X** | Rejected: failed level 1 |

**To be useful to forecasters your observations need to reach S or V.** Level 2
includes the internal consistency check that fails you when dewpoint exceeds
temperature, plus a statistical-spatial check that flags stations failing most
of the time over the preceding week.

To check your own flags, see the validation tools in
[Install, commission and maintain](/docs/weather-stations/commissioning/#validation-tools).