Link naar artikel van de BBC
Met Office and BBC Weather Centre Forecaster John West shares with us his thoughts on what could be causing this effect.
"This is a very unusual phenomenon, but the most likely explanation is that the "fog dome" has been caused by a source of heat close to the ground, possibly an agricultural building or a relatively warm pool of water. As the fog has formed in the valley this heat source has forced the fog to lift away from the ground into a dome as warmer air rises; like a hot air balloon."