On Thu, 20 Jul 2017 20:38:18 +0100, "James Wilkinson Sword"
wrote:

snip

puring with rain all day is nothing like spitting for half an hour.

We know but aren't you only taking notice of a part of the information
on offer?

Yet they don't distinguish between the two.

They do, but not by using the single variable you mention in
isolation.

There should be a measurement where 0% means no rain at all, and 100% means rain all day.

0% is just that, no rain at all that period

'There is a 100% chance of rain' (as the definition of that
prediction) means that it *will* happen (as a prediction) at some time
during that 24 hour period (say) and the *additional information*
will generally determine how hard and for how long it will (is likely)
rain during that same interval.

So, whilst 'There is a 100% chance of rain today' wouldn't be of use
to you in isolation, it would be of use to anyone thinking of watering
their garden or painting their shed 'that day'.

It could rain heavily ... it could rain all morning ... there may just
be light shower in some places ... are examples of the additional
information you weren't considering?

Cheers, T i m