Punta Arenas is a modern, midsized city. It is cold and windy most of the summer. Wind is the key. It is very windy. I can't imagine what it would be like in July, as to just go for a few hours would likely be unpleasant to walk around, although there should be enough open to pass the time. I'd go for an overnight - it is quite a bit of flying (over 3 hours nonstop from SCL each way, and usually you have a PMC stop). Here is the forecast for the next few "balmy" fall days:

Chubascos

Por la noche
Mínima 1°C
Probabilidad de precip.
60%


08 Mayo
Pronóstico

Chubascos

Máxima 4°C
Mínima 0°C
Probabilidad de precip.
40%


09 Mayo
Pronóstico

Chubascos

Máxima 5°C
Mínima 1°C
Probabilidad de precip.
70 %


10 Mayo
Pronóstico

Mayormente nublado

Máxima 4°C
Mínima -1°C
Probabilidad de precip.
10 %