At what altitude does it start to get noticeably cooler?

[BMI]

Originally Posted by Joe90

I live at about 110 metres above a coastal plain (10m), the temperature is actually slightly warmer overall, because the minimums are warmer.

Definitely I can see that.

It's all about cold air drainage.

In some fruit growing regions the apple orchards or orange groves are
located on higher ground, on slopes about the valleys. Both extends the
growing season and milder coldest tempatures.
For example apple orchards in Quebec, around Mont Ste. Hilaire.