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Look at the picture on the opposite page of fog in Frankfurt yesterday (in the weekend print edition of the newspaper, in which this article first appeared – the picture is also on this web page).

If reminds me of lots of weather we have had recently in Northern Ireland. For example flying back from London recently to Belfast there was low and heavy cloud over much of Britain (albeit not low enough to be fog). Then, far above, there lighter cloud, through which blue sky was only visible at points.

This meant that down at ground level there were effectively two layers keeping the sun out. I knew that underneath the clouds it would have been a deep grey day – of the variety I dislike very much.

But this heavy cloud cover or fog is one reason why we have had extraordinarily mild weather this week. . It was 13.7 celsius on Christmas Eve, a respectable spring temperature, when I talked to shoppers in Belfast including Stephen Nolan who were able to wear light clothing, minus a jacket.

Click here for one of the stories I wrote about some of that mild weather. The Met Office explaied that such cloud and fog means it never gets very cold at night or day.

Remarkably, parts of Northern Ireland and Scotland never fell below 11.0 C and 11.9C respectively on Christmas Eve night/Day morning. Neither at 11pm on December 24, nor 4am December 25. That is near to typical NI summer night minimum temps of about 12C, when people feel no need for home heating.

• Ben Lowry (@BenLowry2) is News Letter editor

Ben Lowry: The heavy cloud has helped keep us almost warm at night in Northern Ireland over the Christmas holiday