As far as I know, the rules haven't changed regarding the reporting of mist,
fog or haze.

I personally still use RH of 95% as a guide, but do not stick rigidly to it.
Later this morning for instance, RH may be 92 or 93%, with vis of 3000m.
I would still report mist.
Same thing, when after the clearance of overnight fog, the vis may be 4000m
with RH 92%.
Again, to report mist would be more appropriate.
If humidity falls to 90% this afternoon, then I shall report haze.
I have reported smoke haze with vis below fog limits, when serving in
Germany (10402) back in the late seventies.
With a drift from the Ruhr industrial complex, visibility could fall to less
than 1000m on rare occasions, with RH considerably less than 95%.

(WR)
Have gone into fog here since 0900, with vis now 500m.

Eric Belton