"James Wilkinson Sword" wrote in message
news
On Thu, 20 Jul 2017 16:08:28 +0100, NY wrote:

"James Wilkinson Sword" wrote in message
news
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.

Given that it includes the word "chance" (ie probability) I'd interpret
it
as the second meaning: if (hypothetically) you replayed the day many
times
(Groundhog Day!) then approx 40% of the occurrences of the day would have
some rain.

Which is of no use to me whatsoever.

Bullshit.

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

Sure, but ours gives both the change the range of rainfall in mm
expected and and a flag for thunderstorms too, in 3 hour blocks.
http://www.bom.gov.au/places/nsw/syd...cast/detailed/

Yet they don't distinguish between the two.

Ours does.

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

Better to show the risk in 3 or 1 hour blocks so you can see when
it is likely to rain and how heavily right thru the day and night.