ImPlaneCrazy
If you are talking about Flybe's Q400s, coupled with the bad weather in the Channel islands over the last couple of days then this is what the deal is for us (alot of which has already been said). For CAT II operations the visibility needs to be 300mtrs or better for us to make an approach. The crew, airfield and aeroplane needs to be CAT II capable. For CAT 1 operations (standard ops) the visibility needs to be 550mtrs or greater for us to be able to make an approach. Local restrictions can apply, like some airfields require you to have 800mtrs visibility, or 1000mtrs visibility to be able to make an approach. If you are allowed to make an approach then the height at which you have to be visual is 100ft for CAT II operations, and 200ft for CAT 1 operations.
The Channel Islands are only certified for CAT 1 operations so the visibility required is alot more restrictive. (550mtrs & above), the weather here has not got above 200mtrs (+/-50ft) for the last two days and nothing has gone in or out of there for this period. Yes, you have to conduct a go-around if you have not got any section of the approach lighting visible at 200ft (above aerodrome)
Hope this helps.