This was my experience. Years ago I travelled to New Zealand in what would be their spring time. We stayed in Wanaka but also travelled around Twizel, Tekapo etc.

Although it was pretty sunny with clear blue skies, the air temperature was fairly chilly (shirt, jumper and fleece cold - and I'm Scottish so used to cold weather) and I started to burn. I was warned about this, and the probability of high UV exposure at altitude by the locals and family, and was advised to apply a high factor sunblock whilst roaming around the higher elevations of New Zealand's South Island, which I did.