It's not just snow, also standing water (hydroplaning).
What's the rolling diameter of the stock 14" tire?
If you seriously improve the aerodynamics of the car, one of the side effects is that you'll need to revise the axle ratio, most easily done by oversizing the tire. If your target diameter turns out to be 28" then you qualify for 30% less rolling resistance:
http://ecomodder.com/forum/showthread.php/bridgestone-announces-large-diameter-narrow-tires-25208-9.html#post407899
Compare the BMW i3 bolt diameter to you car's. Fitting 19" wheels is the trick. The whole 16-page thread is here:
http://ecomodder.com/forum/showthrea...res-25208.html