In article ,
Waghorn writes:
OK, so the WMO are a bit slow on this - but why use out of date
averages when talking to the UK public about the UK? Seems plain daft
to me.

Stoopid question-why use 30 yr averages.Why not extend the reference period decadally as new data
becomes available?

Because our climate isn't constant. There therefore has to be a
trade-off between having a period long enough to iron out most of the
year on year random variations but one short enough to be representative
of the current climate. Presumably it has been decided that 30 years is
a reasonable compromise.
--
John Hall
"If a man will begin with certainties, he shall end in doubts;
but if he will be content to begin with doubts,
he shall end in certainties." Francis Bacon (1561-1626)