With alternates (or TAFs). Easy if you're IFR.
Seriously though,
Jay Bo and Nik
I hope you are not insinuating that you are allowed to pick and choose Area Forecast applicability based on TAFs?
At night, can you say the TAF for an aerodrome on the other side of my area says not enough cloud for an alternate, therefore I can disregard the cloud that is forecast below my LSALT (any cloud is enough to cause a problem if you fly into it...easy to do on a moonless night) for the rest of the area?
Admittedly, this is more of a NVFR scenario. During the day, you see the area of reducing vis to either avoid it or turn back, bit harder to do at night.