Well, apparently GSX expects precipiation to offer de-icing although that is not mentioned in the manual (I found that out once I turned on precipitation).
I've probably flown out of my local Canadian airport at least 20-30 times in winter (might be even more), many times blue sky and not a cloud in the sky and yet we did de-icing. Actually my last winter flight was in January, the flight left at 10:15 with nice blue skies and we had to de-ice. Why? Temperature at 10:15 was still in the minus and the plane stood on the tarmac overnight with temperatures probably around -10 to -15. The plane had probably accumulated some frost enough to warrant de-icing (my airport handles anything from Dash8's to A330/B767/B747's).
Truth told, there is hardly a flight in winter that doesn't get de-icing where I live with the large majority not having any precipitation. So in my opinion it would be better to just offer de-icing <4C (precipitation or not) and let the captain decide.
Granted there is any easy workaround for me. Before pushback I load an icing weather situation in AS2016, request pushback with de-ing and then go back to the actual weather but I would prefer not having to do that.
Andre
(overall very happy with GSX, great product!)