Weather Conditions

1) Atmospheric moisture (humidity)

•         Minimum moisture in air required for snow formation
•         Higher humidity means greater amount of water in the air

2) Atmospheric temperature

•     Atmospheric temperature must be at or below the freezing temperatures
• Freezing:  0 Celsius or 32 Fahrenheit
•     Decreased temperature compacts air molecules, removing water for icy crystal uptake

Fall: Snow or mush?

•     Ground temperature must at freezing or appropriately cool conditions
•     If air temperature as snow falls is warm enough, it will melt

The process: Ice crystals form in the atmosphere when there is sufficient moisture in the air. As these ice crystals fall through the clouds and atmosphere, they absorb water in the air, stick together, and fall as snow if heavy enough. If air temperature near the ground is cool enough, snow will fall as.... well, snow and if it's warm then it will melt.

Too cold or warm to snow?
It can be too warm to snow, but never too cold to snow. Why does it rarely snow in extremely cold, but dry regions? The key is in the combination of temperature and moisture. Moisture is low in dry regions, therefore even if it is cold enough to snow, it's not humid enough. Moisture in the atmosphere is necessary in the formation of ice crystals, which are basically the foundation of snow.