BOAC:
a) your point is noted -however remember how the authorities quoted FOB figures to the EXACT digit to claim whether or not the 3 FR diversions had complied with the rules. Such accuracy is a nonsense.
d) I was simply using the wx analogy to illustrate what happens in very busy TMAs when something goes wrong - not necessarily weather related. In my opinion the fact that most airlines structure their fuel policies around only weather means that there is a higher risk of crews being caught out in the summer when they "are not required to carry extra fuel."
In the 70's when I operated B707 freighters to African destinations with a fuel policy that allowed single runway + no Alternate - I was unfortunate to be caught twice with blocked runways ( both of which were cleared in time, fortunately )
My personal "bitch" is with company fuel policies which encourage crews to "commit" to single runway destinations when they really should have sensible destination holding fuel. I personally have had many more diversions due to blocked runways rather than weather diversions. Perhaps your experience is different?
I do not have a single extra figure: there are too many differing situations for that.