ORIGINAL: Gray Beard
You won't even notice the difference. I almost never have to change a needle setting unless it goes from the 70s to the 20s or 30s. Watching needle twisters drives me nuts, an engine doesn't notice 20 degrees other then the cold start first thing in the morning.
I know you're just talking about changes in weather and not fuel
I only noticed my needle needing an adjustment at the end of the summer when it was, like you said, dipping from the 70's to the 40's.
Switching to 15% will require the needle to be opened to prevent lean run, as more nitro likes less air.