On 25/07/17 11:55, whisky-dave wrote:
On Thursday, 20 July 2017 20:38:25 UTC+1, James Wilkinson Sword wrote:
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. Pouring with rain all day is nothing like spitting for half an hour. Yet they don't distinguish between the two.

How about showers or inteminant showers or heavy downfalls, storms.

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

So what would 50% mean light showers for 50% of the day or heavy rain 50% of the day, and whayt would the other 50% be of the day be like ?

Weather forcecasts these days are the output of models. So it's the 50%
probability of the model being right. The further into the future the
forecast, the less its predictability; after the event you can assess
the accuracy and, based on that, estimate the accuracy of future
forecasts. So 50% chance of rain = don't know, maybe yes maybe no. 95%
if it doesn't it's a freak, 5% if it does it's a freak.


--
djc

(–€Ì¿Ä¹Ì¯–€Ì¿ Ì¿)
No low-hanging fruit, just a lot of small berries up a tall tree.