I'm not sure about others - but I've even gone naked up in the hills when its been snowing. Ovbiously not for too long but its still nice to feel the open air against my skin. My advice - take a warm fleece or something and put on when you get too cold. Naturism can still be enjoyed in most weathers - not just the summer. In some ways even more so - as you are far less likely to meet non naturists.