Sometimes the diversions can be due to poor operations planning. About 3 years ago I was maintenance for Flybe at SOU.
One evening at around 2000 just as the last departures took off the fog arrived as forecast. I took a look at the BBC weather and saw that at around 2200 they were showing a little bit of wind picking up and I thought, "That will lift the fog".
We watched the flight tracker as the inbounds all went into the hold. One by one they diverted to EXT, BHX. BRS, CDF. Just as the last one landed at BRS I looked out of the window and could see the runway, the RVR was at least 800m. It was too late for the 8 diverted aircraft to get airborne again. Very big cost in transport and reputation.
If I could see the possible improvement in the vis why couldn't Flybe ops. the met men or the crews? A delay of about 1/2 hour in the departures would have got all 8 aircraft in at SOU. Airport closes at 2300 or 2330.
For info, I did 20 years night freighting around Europe and got a lot of experience of spring and autumn fogs.