in weks or for weeks

[EndlessHope]

Hello,

It hasn't rained in weeks and when it finally did, I was asleep.
Or,
It hasn't rained for weeks and when it finally did, I was asleep.

Thank you.
Endless Hope

[Mister Micawber]

Both prepositions are fine and synonymous, but your verb tenses are awry.

It hadn't rained in weeks and when it finally did, I was asleep.
Or,
It hadn't rained for weeks and when it finally did, I was asleep.
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Native English teacher at Mister Micawber's

[EndlessHope]

Thanks, one more question though, why it's "hadn't" not "hasn't". What difference in meaning doese it make?

[Mister Micawber]

Past perfect because the absence of rain came before the 'finally did', which is a past event succeeding the past absence of rain-- that is is the use of the past perfect. Present perfect talks about events related to the present, and nothing in your sentence relates to the present.
_________________
Native English teacher at Mister Micawber's