The sun is out, but it's cool.
'Fresco' — FRES-co. Stress on the first syllable. Short, crisp word. Don't confuse with 'freddo' (cold) — fresco is pleasantly cool.
Use on days when the sun shines but the temperature is mild — common in spring and autumn in Italy. 'Fresco' (cool) is a positive term, unlike 'freddo' (cold) which is a complaint.
'Fresco' means cool or fresh — it's a pleasant word, not a complaint. 'Fa fresco' = 'it's cool'. This contrasts with 'fa freddo' (it's cold) which implies discomfort. The distinction between 'fresco' and 'freddo' is important for expressing whether you're comfortable or not.
Una bella giornata fresca.
A lovely fresh day.
Positive framing — 'fresca' as agreeable rather than something to complain about
C'è aria fresca.
There's fresh air.
Focus on the quality of the air — refreshing rather than cold
Non fa né caldo né freddo.
It's neither hot nor cold.
Neutral assessment — describes a perfectly temperate day
The recommendation to take a jacket ('prendi la giacca') is one of the most universally Italian pieces of advice — dispensed by mothers, grandmothers, and older neighbours regardless of actual temperature. It's an act of care as much as meteorology.