20% chance of rain before noon

Question

"20% chance of rain before noon", that's what the weatherman said this morning.

But, strictly speaking, shouldn't that be "100%"?
For consider:
It's certainly rained in the past. One only has to mention Noah for proof.

And "before noon" includes the past.
Therefore, it's certain it's rained before noon!
Where and how, grammatically speaking, is it implied in that phrase that the meaning is "before noon but later than now"?
Does the word "chance" do it?
Or is the phrase shorthand for "there's a 20% chance that it will rain before noon"?
Bob G

Usenet · Accepted Answer

Bob G wrote on 11 Aug 2004:
[nq:1]"20% chance of rain before noon", that's what the weatherman said this morning. But, strictly speaking, shouldn't that be "100%"? For consider: It's certainly rained in the past. One only has to mention Noah for proof. And "before noon" includes the past.[/nq]
"before noon" does not include the past. You are mistaken. Consider, the scenario in which it rained between midnight a 6 a.m.; it is now
7 a.m. When the weatherman says "There's a 20% chance of rain beforenoon" at 7 a.m., he means that there's a 1-in-5 probability that it will preciptate between now and noon.
[nq:1]Therefore, it's certain it's rained before noon![/nq]
You are using the form of logical statement without the substance.
[nq:1]Where and how, grammatically speaking, is it implied in that phrase that the meaning is "before noon but later than now"?[/nq]
You have to look at the semantics of the sentence, idiomaticity, and common sense. The grammar that implies future ("before noon") rain is in the tense: "There is a 20% chance". Even if the "There is" is elided, it is implied.
[nq:1]Does the word "chance" do it?[/nq]
No.
[nq:1]Or is the phrase shorthand for "there's a 20% chance that it will rain before noon"?[/nq]
You are so confused that your discussion and questions have confused me.
When the weatherman says "There's a 20% chance of rain before noon", he means that the probability that it will precipitate between midnight and noon on (DATE) is one in five. It has nothing to do with what happened during Noah's time

Franke: EFL teacher & medical editor.
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Usenet · Answer

[nq:1]"20% chance of rain before noon", that's what the weatherman said this morning. But, strictly speaking, shouldn't that be "100%"? ... only has to mention Noah for proof. And "before noon" includes the past. Therefore, it's certain it's rained before noon![/nq]
So you'd accept without hesitation my assertion that the Duke of Normandy will become King of England before noon?

John Dean
Oxford

Usenet · Answer

[nq:2]"20% chance of rain before noon", that's what the weatherman ... includes the past. Therefore, it's certain it's rained before noon![/nq]
[nq:1]So you'd accept without hesitation my assertion that the Duke of Normandy will become King of England before noon?[/nq]
I would. Without even checking the newspaper to see if there was something going on in the UK that I wasn't aware of. Mind you, if the statement was made by anyone except John Dean, I'd be a bit dubious.

Usenet · Answer

[nq:1]"20% chance of rain before noon", that's what the weatherman said this morning. But, strictly speaking, shouldn't that be "100%"? ... and how, grammatically speaking, is it implied in that phrase that the meaning is "before noon but later than now"?[/nq]
It's not implied grammatically; it's implied semantically.

Mike Nitabach

Usenet · Answer

[nq:2]"20% chance of rain before noon", that's what the weatherman ... includes the past. Therefore, it's certain it's rained before noon![/nq]
[nq:1]So you'd accept without hesitation my assertion that the Duke of Normandy will become King of England before noon? [/nq]
Well, no!
First, your statement has the segment "will become" in it, whereas it does not appear in the weatherman's statement. So the two are not quite parallel.

If we amend your statement to read, "there's a 20% chance of the Duke... being king before noon", you will be closer in structure.

My English History is weak, has the good Duke ever been king?

If he hasn't, then the amended statement has no logical certainty.

But if he has, then the statement should read "100%".

My guess, as I stated in the original post, is that the weatherman's pronouncement is taken as shorthand for, "...20% chance it will rain before noon". the future tense being inferred.
Bob G

Usenet · Answer

[nq:1]Where and how, grammatically speaking, is it implied in that phrase thatthe meaning is "before noon but later than now"?[/nq]
If you are listening to a weather forecast to learn about the past then grammar shouldn't be your main worry.
Paul

Usenet · Answer

Isn't it more to the point to ask whether the forecast probability refers to the area for which the forecast is issued as a whole, or to any given spot within that area?

Paul
In bocca al Lupo!

Usenet · Answer

[nq:1]Isn't it more to the point to ask whether the forecast probability refers to the area for which the forecast is issued as a whole, or to any given spot within that area?[/nq]
Neither. A 20 % probability of rain means that it had rained on 20 percent of all the observed days which had the same meteorological conditions like humidity, air pressure and the like.

Best regards
Steffen

Usenet · Answer

[nq:2]Isn't it more to the point to ask whether the ... a whole, or to any given spot within that area?[/nq]
[nq:1]Neither. A 20 % probability of rain means that it had rained on 20 percent of all the observed days which had the same meteorological conditions like humidity, air pressure and the like.[/nq]
But for what values of "same"?
Anyway, surely it's not just a statistical analysis of previously observed days.
It's more like "if the conditions that we observe now were to be repeated for the next 10 days, we would expect it to rain on 2 of those days". Obviously if metereologists were capable of observing exactly all the relevant data to an extremely high precision, and understood exactly how to determine if those conditions would cause rain, figures like 20% would never happen - it would either be 99% or above or 1% or below.

Usenet · Answer

[nq:2]Neither. A 20 % probability of rain means that it ... same meteorological conditions like humidity, air pressure and the like.[/nq]
[nq:1]But for what values of "same"? Anyway, surely it's not just a statistical analysis of previously observed days. It's more ... were to be repeated for the next 10 days, we would expect it to rain on 2 of those days".[/nq]
Right. Except that the "next" should be omitted. It's basically, "the best we can say is that if the same observable conditions were to arise on multiple days, 20% of them would be expected to have rain". To evaluate such predictions, you essentially look at all the times they said "20% chance of rain" and see how often it rained. The closer to 20% of the time, the better.
Probably the most common scoring function used to evaluate such predictions called the Brier Score, which is simply the sum of the square of the difference between the predicted probability and the actual "probability" (zero or one). The lower the score, the better.

Of course, it probably largely is based on a statistical analysis of previously observed days. Not simply those that had "the same meteorological conditions", though, but also those that had (to varying degrees) "similar meteorological conditions".

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20% chance of rain before noon

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