We're having our usual beautiful Sydney winter right now ... 22 degrees C, no wind, blue skies, warm sun.
My office is actually a sun-room with large windows on 3 sides, glorious in winter, horrid in summer. I typically abandon my office when it reaches 30 degrees C or so with the portable aircon running (usually 38+ degrees C outside) ... retreat to a cooler room, even if it is less convenient to work in. Less productivity is better than no productivity!