The fog blanketing parts of the UK is known to meteorologists as radiation fog. It has nothing to do with radioactivity, though.
Common in the winter, radiation fog builds when the land cools under clear night skies by thermal radiation. As the ground chills, so does the air directly above. And since cooler air holds less moisture, the further the temperature drops, the more moisture condenses to form layers of fog.
Several factors have combined to make the fog particularly thick. First, many parts of England had plenty of rain last week, making the ground moist. The warm daytime temperatures mean the air can hold more moisture than usual for November, so there is more to condense at night.
Added to that is the high pressure system over Britain, which has brought clear skies, making for cold nights and very little wind to disperse the fog. Radiation fog normally lifts in the early morning when the sun rises and warms the ground. But thick fog can block much of the warming, causing it to hang around until noon or longer.
Emma Sharples, a Met Office meteorologist, said there were two factors contributing to the fog formation. Light winds and high pressure are dominating northern Europe at the moment, while a lot of rain last week means that the ground is very damp.
“Fog is like a cloud on the ground and when you have cool air the moisture condenses,” Sharples said. “Because there is light wind, it’s not being blown away.”
The Met Office said Monday would be the last night of extensive fog, as cloud, rain and wind move in from the south to disrupt what had been perfect conditions for it to form.
