I don't need to say that if there is no more rain, then only we will go out for a dinner.
How do I use "needless to say" in such a sentences?
Needless to say, if there is no more rain, then only we will go out for a dinner.
"Needless to say" means the same as obviously when placed at the beginning of a satement.
It is either used as hedging, i.e. the speaker makes the statement but points out that they think it's obvious just in case the statement really is obvious, or it is used to boost the speaker's ego, i.e. the statement might not be obvious but they make it seem like it is to make the listener think that the speaker is clever.
The height a body of water is affected by gravity, so the more mass land has the more an ocean is pulled towards it. Needless to say, because of this, the melt water from the Greenland icesheets will cause higher water levels in the southern hemisphere, while lowering the water levels in the nothern hemisphere.
As you can see "needless to say" is normally put before, or within, some concluding statement.
You could also use it parenthetically:
It is, needless to say, very cold in November.