In article
,
Graham Easterling writes:
On Jan 7, 5:34*pm, "Ian Bingham"
wrote:
My average temperature graph for January (1990-2010) shows low temperatures
at the beginning and end of the month and relatively high temperatures at
mid-month. *This appears to be due to the fact that every year in January we
seem to get a few days of more or less strong SWlies which of course raises
the temperature appreciably. *This has occurred at various times of the
month, so the average puts it in the middle, I suppose. *For example I have
as 21-year means:
Jan 1st * 2.1C
Jan 15th *4.4C
Jan 31st * 2.3C

Ian Bingham,
Inchmarlo, Aberdeenshire.

A very similar pattern here over the 20 years of my records. In fact
the 15th is the mildest day of the month with a mean temperature of
8.2C.

There are marked colder spells each side, the low points being:-

8th 6.7C
26th 6.2C - The coldest day of the winter over 20 years.

Graham
Penzance

The tendency for mild and cold periods in January to occur around the
same dates in many years reminded me of the old idea of "singularities",
investigated for the UK by CEP Brooks and HH Lamb. A websearch led me to
this newsgroup's excellent FAQ developed by Martin Rowley:

http://weatherfaqs.org.uk/node/179

Brooks was looking at 1889-1940, but the mid January mildness in recent
decades would fit in very well with his identification of a "stormy"
period that occurred on average from Jan 5th - Jan 17th and peaked on
Jan 8th, which was observed in 45 years out of 52. (Assuming that in
winter stormy periods will usually be mild.)

The relative coldness around the 26th wouldn't tie in so well. Although
the period 18th - Jan 24th was generally anticyclonic, Jan 24th - Feb
1st reverted to "stormy".

Lamb's analysis was broadly similar.
--
John Hall
"I look upon it, that he who does not mind his belly,
will hardly mind anything else."
Dr Samuel Johnson (1709-84)