(I hope this is not dupe posting; I did not see it elsewhere)
Fog in Barcelona on Dec 23rd 2012 overwhelmes ATC: "Let the aircraft land and put them on taxiways, carpark, roof ... but on the ground!"
Spain was under the influence of a large high pressure system. The day in Barcelona had thus been clear, the high humidity however created increasing fog in the evening requiring low visibility procedures invoked at Barcelona Airport leaving only runway 25R available for approaches. As result more and more aircraft needed to be sent into holds around Barcelona, the approach frequency became more and more busy until there were transmissions nearly without any interruptions around 20:15L (19:15Z)..."
The Av Herald article notes that this is not the first time that Spanish ATC has had staffing issues. Some European tabloid papers ran "Chaos in the Skies" type stories over this breakdown in the normal routine and several diversion.