Do you deduct weight for Low Vis Ops?
 

So we get a reduction of 7,400 kg for Ops below D/H 200ft and a further 2,800 kg. if the OAT is <8deg C., from max Ldg Wt. on the B737-300.

Question - does your airline apply these penalties concurrently, cumulatively or maybe not at all?

Yes..cumulatively