Randomair,
When you get your wx/notams etc at the briefing stage, do they provide you with a OCH for the approaches in use?? if they do presumably you just compare that with the system minima that your using for planning?
You are given a double-sided A4 sheet of all the airfields you are likely to use and the DA/MDA for each available approach.
It becomes fairly obvious that you can't use some of the flight planned diversions because they are below the weather minima.
Good luck!