When my brothers were babies, I remember my mother feeding them in the afternoon, putting the in the pram, wrapping them up then leaving them outdoors to sleep for an hour or two. She did this every day with all of us as babies, whether there was rain or snow (though I wouldn't imagine she did if there was gale force winds!) but the pram was always sheltered. This was encouraged as it's supposed to strengthen the baby's immune system. I must admit I never took an antibiotic until I was 11 years old, so I believe there's some truth in that theory.
The reason I ask is that recently in Dublin a woman in Dublin was reported to the police for leaving a baby she was minding sleeping in it's carrycot on a balcony. This lady, who was minding her grandchild, was from Scandinavia and this is apparently a normal practice over there (and the temperatures are much lower there!!).
At the moment the weather is mild here and I'm letting DD2 sleep outdoors in the afternoon, though she never sleeps more than half an hour during the day! I live in the country, and don't think I'd do it if I was living in a town.