Is this sentence ok without "or not"?

[Nessie]

Whether we go out will depend on the weather
=> Is the above sentence all right without "or not"? By the way, if we use "upon" instead of "on" in that sentence, will it sound more formal?

Thanks a lot
Nessie
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... something we never have again, I know... I guess I really really know..

Sorry seems to be the hardest word...

[Yankee]

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I'd say 'or not' is optional. However, I'd also say that isn't exactly the most elegant sentence ever written.

Yes, saying 'depend upon' generally sounds more formal than 'depend on'.
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