[Grammar] It shouldn't rain tomorrow.

Can I say "It shouldn't rain tomorrow"? Can negative should express (lack of) probability?

You will hear it in BrE, to mean "It's not forecast to rain tomorrow [but of course the weather forecast isn't infallible]".

englishhobby said:

Can I say "It shouldn't rain tomorrow"? Can negative should express (lack of) probability?

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Americans would say ​It's not supposed to rain tomorrow. "Not supposed to" and "shouldn't" are generally synonyms, but in this case, shouldn't​ doesn't work in AmE.

emsr2d2 said:

You will hear it in BrE, to mean "It's not forecast to rain tomorrow [but of course the weather forecast isn't infallible]".

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GoesStation said:

Americans would say ​It's not supposed to rain tomorrow. "Not supposed to" and "shouldn't" are generally synonyms, but in this case, shouldn't​ doesn't work in AmE.

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Can the same answers be applied to using oughtn't to in the same situation (with rain) in BrE and AmE?

No. The verb 'ought (not)' implies that the rain has got a choice in the matter, as in 'I oughtn't to have that extra glass of wine before driving.'

englishhobby said:

Can the same answers be applied to using oughtn't to in the same situation (with rain) in BrE and AmE?

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Oughtn't really doesn't exist in AmE. We say shouldn't or, sometimes, ought not.

GoesStation said:

Oughtn't really doesn't exist in AmE. We say shouldn't or, sometimes, ought not.

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So, can ought not replace shouldn't in this context?

englishhobby said:

So, can ought not replace shouldn't in this context?

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Not in AmE because a) we don't use oughtn't and b) we don't use shouldn't​ in this context.