It is an inverse statement, which is not necessarily true. It is one of the laws of logic and logical reasoning.What makes it illogical is:It may be cold but not cold enough.It can be too cold to snow.The air may be dry; without moisture, it will not snow.It may have snowed before and it may snow later, but it is not snowing now.It may be cold without snow falling because the temp is warming.It may be cold without snow falling because it is raining.It may be cold without snow falling because sleet is falling instead.