NSC (No Significant Cloud) is used when there are no “clouds of operational significance” to report – no CB or TCU, but CAVOK is not appropriate (either ceiling, visibility or any significant weather not meeting CAVOK requirement).
CLOUD OF OPERATIONAL SIGNIFICANCE —
- A cloud with the height of cloud base:
a) below 1500m (< 5000ft); OR
b) below the highest minimum sector altitude
a) or b) – whichever is greater,OR
- a cumulonimbus cloud (CB) at any height; OR
- a towering cumulus cloud (TCU) at any height