On 20/07/2017 12:25, James Wilkinson Sword wrote:
On Thu, 20 Jul 2017 12:22:20 +0100, Ash Burton
wrote:

On 20/07/2017 12:13, James Wilkinson Sword wrote:
What do you believe weather forecasters mean when they say "40% chance
of rain"?

1) It will rain for 40% of the day.
2) There's a 40% chance it will rain at some point.

I googled it and apparently it depends on the forecaster? 1) and 2) are
completely different meanings.

I think it means 2

So pretty useless then. I have no idea if it will be for 20 minutes or
the entire day.

Pretty useful actually. If it is likely to rain, you know not to go out
without a coat or umbrella, drive an open topped car or start an outdoor
event that could instead take place indoors. It matters little whether
it rains for 20 minutes or all day if you are going to get soaked pat
way through.

You are correct that there are many other things where the period it
will rain for is more useful than the likelihood though.

SteveW