The Laws of Blessings which apply during the Rainy Period (24)

1. It is permitted to walk on snow, even if he causes the snow to melt and dissolve, as he has no intention to do this, and it is impossible to avoid it. (Shulchan Aruch and Mishne Berurah 320)

2. If one has a new garment or a garment which looks like new (and one would normally be careful to keep it clean and dry) upon which snow fell on Shabbos and had not yet melted, one may shake it gently but not strongly. However, a raincoat made from plastic without any cloth at all, may be shaken even powerfully to remove the snow. (Shemiras Shabbos Kehilchasah 15:39)