We have added weather system to out mid-term list, and it's one we're excited about. It will support snow, rain, hailstone, wind, storm and desert heat (currently list subject to change) and should be as easy as selecting a drop down from a slider box or adding a single command in script.
PC SPECS: Windows 7 Ultimate 64-bit, Intel Core i7 920 (PASSMARK:5008), NVIDIA Geforce 9600 GT GPU (PASSMARK:752) , 6GB RAM