The late Colin Finch ( a passionate weather enthusiast, who died in his
late fifties in 1991) was always on the alert to find links between the
weather in one season and the next. One of them , which he devised in the
early 1970s, was an apparent correlation between maximum temperatures in
the second week of July in Surrey and the rest of the summer. He called it
his 75f + rule. He calculated that if the temperature failed to reach 75f
during that week, the rest of the summer would be cool; and if there were
more than 2 days with the max above 75f then many more warm days would
follow.
I have continued to follow his 'rule' since he died but have modified it
slightly.
The figures for the years 1971 - 2004 are :-

No of 24c+ days average no of 24c+ days
7 - 14 July 15 July - 31 August

3 days or less 12.3
4 days or more 25.0

The figures show that when 24c has been reached on at least 4 days in the
second week of July, the following 6 weeks ( the peak summer holiday weeks)
have produced, on average, twice as many warm days as those years when 24c
has been achieved on 3 days or less during the critical week. This year has
produced 5 24c+ days between 7 and 14 July.
Peter Clarke
Ewell, Epsom 55m

Biographical Note:
Colin Finch, when I first knew him in the 1960s, used to get up very early
in the morning on working days to plot a weather chart ( before he left home
for his office) of the North Atlantic/ Europe from morse code broadcasts on
a short wave radio. On Saturdays he would spend most of the day plotting a
Northern Hemisphere chart by the same method.
In 1970, when Radio London began broadcasting, he was interviewed on its
Breakfast programme each Friday morning, by which time he would have
plotted an Atlantic synoptic chart by hand.