LEM - it would help if you could give us:-
The minima for each runway - are they VISIBILITY or RVR based?
The reported visibilty (RVR?) for both runways.
(PS was it PRN?)
It can happen that the met office or tower is sitting in a fog bank while the real airfield basks in warm sunshine!
Happened to me in BCN once with sea fog around the tower. 10k+on all runways except 02.