Actually, we know quite a bit about the formation and conditions of snow. Why it falls, when, where, how much, with what consistency, why it is 'wet' or 'dry', why it is sleet or hail or ice... It has to do with the freezing point, temperature, humidity of the regional airmass, condensation, and stuff - not having much experience with the stuff I would be at a loss to explain it more precisely, but there are those who can.
As to molecules and such, it's water. H2O. Two hydrogen, one oxygen, it freezes and crystalizes. Not too tough. Subatomically, Hydrogen is (usually) an electron and a proton. Oxygen has (usually) 8 of each, plus 8 neutrons. If you want to know more about snow at the subatomic level, you could ask Physicist. But I'm not sure what more you want to know about it.
There is the additional point that your criticism applies equally strongly to everything - if we are uncertain about any aspect of particle physics, I suppose we don't "truly understand" the universe. But again, would you have us teach nothing to anyone? We'd certainly have to throw out the Bible with the bathwater.