Why does snow fall instead of rain?

Snow falls instead of rain when frozen crystals can travel from the cloud to the ground without melting. The same water could become raindrops if it passed through warmer air, so the layers of temperature between cloud and sidewalk decide what reaches you.

Many drops begin high above as ice, even during warm storms. If the air below is cold enough, crystals join into flakes; if it is barely cold, they arrive sticky and heavy, the kind that packs well in mittened hands.