JJCMayes1 wrote:



However, there have been some warmer nights (21-09h minimum). Whereas all
official records are for the 24 hours ended 0900hr, records prior to 1982
at met office synoptic and auxiliary stations were reported in 12 hour
increments,
later years saw them standardise to 24hr minima. In 1983 they published
both the 12 and 24 hour minima (by mistake!) and this produces some
alarming disparities .... at Heathrow on July 16th 1983 the 12 hour min.
was 25.3, a value equalled by Cilfynedd (in the Taff valley by Pontypridd;
trapping of long wave radiation in the deep valley??). The 24 hour minima
were much lower in both cases (the previous morning must have been cooler
than this, hardly surprising).

Not being at home, I can't reply in detail, but I'm pretty sure that
the 1983 "mistake" in the MWR resulted in them publishing the 09-21 min
as the 12-hour min, which obviously will give much higher values. I also
think the chance of missing a high night min in summer because of the 09-09
period is significantly smaller than one in three. The August 1990 Brighton
figure is accepted as the UK record before this year.

One other small point ... pedants will jump on this, so I thought I'd get
in first ... the Channel Islands are not parts of the UK. :-)

Philip Eden