I've retrieved my met notes what I lent to somebody.
CAVOK
The Viz, RVR, weather and cloud group can be replaced by CAVOK if:
1. Viz 10km or more;
2. No cloud below 5000ft aal or below highest MSA, whichever is the highest;
3. No CBs; and
4. No precip, TS, shallow fog or low drifting snow.
I have a passing recollection from a year ago about an additional caveat "..or forecast".
NSC
No cloud below 5000ft aal or highest MSA, whichever is higest and no CB.
Thus the CAVOK definition is more stringent in terms of viz (horiz) and the items in line 4 (and maybe the 'or forecast' point which I only remember but cannot now find 'in writing')
h-r
