From my experience thus far, ice and steel types seem to be the rarest 'mons in the game after Dragon. As such, even during snow their spawn rate remains abysmal at best. I had some snow today and all that I found was a skarmory, which seems to be the most common steel-type in my area, as I generally find 1-2 a week. Off the top of my head, assuming Spheal isn't released yet it MIGHT be a semi-common ice-type that would start showing up in snow.
"Dynamic" Weather System?
So I am really enjoying this new update with weather and gen 3 Pokemon but something is weird. I am expericing snow right now and I have not found any snow and steel type around except 2 swinubs and a sneasel. What the heck. At least give me a magnemite or a jynx. I'm so confused why I found 3 ice types when they are "boosted". The thing with the weather system earlier worked fine. Could it be the rarity of the types of the Pokemon or is something wrong with the game.
Answers
You're not the only one. There's snow around my area, as well, but I've only ran into one Steel Pokémon, which was Skarmory. Other than that, no Ice or other Steel types.
It probably does have to with the rarity of the types, because I rarely see ice types even without snowy weather, and there aren't many Steel types to begin with. I'm hoping Aron, or even Lapras, might show up around here from snowy weather. As for Beldum, we'll have to wait for him to roll out with the second half of Gen 3 that's not in the game yet.