Gillespie field, in the absence of evidence to the contrary we must assume there was proper flight planning. In any case the wx at possible diversion airports are available from ATC.
My point really is that when they departed Belfast there must have been an expectation that the fog would be either lifting or gone by the time they got there. I'd like to see the TAF as it would give an insight. But the fog had not lifted and after two approaches they went into a hold for twenty minutes and made a third approach.
We cannot assume they were running low on fuel and this was a desperate attempt to get in. We have to assume they knew their fuel state and the final approach was either the last attempt before diverting or they believed conditions had improved sufficiently to make the attempt worthwhile.
I don't want to speculate beyond that and in any case the full facts will come out.