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This is a tricky question! Grammatically, it is OK, but logically it sounds a bit weird.
You can say: I'm not working this week, I'm on holiday.This means during the whole week you haven't worked, you are not working, and you will not work. You know this for sure.
It isn't raining this week means that you know for sure that it will not rain the rest of the week. Since we can't predict the weather with this certainty, we do not use this expression. On the last day of the week, we would say, It hasn't rained this week. (past time).
It is OK to say: It isn't raining today. or It hasn't rained today - because we can see what the weather will be for just one day.
It's not going to rain this week. (This is usually as prediction from the weatherman, or your hope.) I hope it's not going to rain this week, because that would spoil my vacation.