On Fri, 23 Jan 2004 16:46:29 -0000, Philip Eden wrote in

snip
There was an article in 'Weather' in the mid-80s (I think) on the
factors required to produce very low minima in the UK
by Roach and Brownscombe. One of their conclusions was
that widespread lows below minus 10 almost always require
a snow-cover, preferably fresh and reasonably deep. It was
a rather patronising article, I remember thinking, and I trawled
the MWR and DWR for every occasion since 1945 when
a temperature of -10 or below was recorded with a less than
50% snow cover; I drafted a sarcastic Letter to the Editor, but
(probably wisely) never sent it. I think I found about 20 examples
in 40 years, but only 3 or 4 of these could reasonably have been
described as "widespread", and many of the others were
isolated observations at well-known frost-prone sites.

An added factor, if we do get low air temps next week, would be the
abnormally warm soil for January. The upward heat flux would make such low
temps unlikely over bare ground. If the cold spell were to be prolonged,
then clearly the soil would cool and lower minima would ensue.

I recall my lowest air temp here without snow over a 30 year period was
about -7C, but with snow was about -13C.

--
Mike 55.13°N 6.69°W Coleraine posted to uk.sci.weather 23/01/2004 17:39:53 UTC