[Jeff22]

Pick up just about any of the good instruction manuals about combat shooting written in the last 15 or 20 years and they will contain photos and written descriptions of how to perform a tactical reload. It's a useful secondary skill to know and would solve your problems with dropping mags into the snow.

Basically, to perform a tactical reload you access your spare magazine, holding it in your fingers. Drop the empty or partially expended magazine into the palm of your support hand and insert the fresh magazine with the fingers of your support hand, and then place the empty or partially expended magazine into your pocket. You have just recharged your gun without dropping a magazine on the ground.

A reload with retention involves ejecting the empty or partially expended magazine into your support hand, putting that magazine into your pocket, and then reloading with your spare magazine out of your magazine holder.
If you have small hands and wide magazines, this might be the better option.

I probably haven't explained the procedure very well. It's easier to do than it is to read about! In real life, these reloads would only be performed behind cover, usually after the initial exchange of shots and when you have "broke contact" and retreated to cover to continue the fight.

If you want to practice the "emergency" or "reactive" reload where you eject the magazine from the gun and then reload, like the previous post said, placing an old blanket or something on the ground works pretty well. It's not a bad idea to protect your magazines from damage when conducting stationary shooting drills anyway -- dropping them on a hard surface is hard on the floor plates and the magazine lips, and dropping them in mud or snow or sand may render them unusable without cleaning.