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.