Incidentally I think we called it "Haar" when I was a lad in
Lincolnshire?
We don't seem to have a name for it down here in the SE (or in Kent at
least). "Up north" (ie from Essex northwards) I'm sure there are a number of
different terms - clag, haar, fret etc.

Whatever it's called, I've been enjoying it - I like cold weather at any
time of year.