What is how cold does it have to be to snow?

It's a common misconception that it needs to be below freezing (0°C or 32°F) at ground level for it to snow. While that is often the case, the actual temperature requirement is more nuanced.

• Atmospheric Temperature Profile: The crucial factor is the temperature profile of the entire atmospheric column, not just the surface temperature. https://www.wikiwhat.page/kavramlar/Atmospheric%20Temperature%20Profile

• Snowflake Formation: For snowflakes to form, there needs to be a layer of air in the clouds where the temperature is at or below freezing. This allows water vapor to crystallize into ice crystals. https://www.wikiwhat.page/kavramlar/Snowflake%20Formation

• Melting Layer: The biggest determinant of whether snow reaches the ground is the presence of a warm layer (above freezing) between the cloud and the surface. If a warm layer exists, snowflakes may melt as they fall through it, turning into rain or sleet. https://www.wikiwhat.page/kavramlar/Melting%20Layer

• Surface Temperature: It can snow even when the surface temperature is slightly above freezing (e.g., 1-2°C or 34-36°F). This is possible if the melting layer is shallow and the snowflakes are large enough to reach the ground before completely melting, or if the ground itself is cold enough to cool the melted snow and refreeze it. https://www.wikiwhat.page/kavramlar/Surface%20Temperature

• Evaporative Cooling: If the air is very dry, falling snow can cool the air through evaporation, which can allow the surface temperature to drop enough for snow to accumulate. https://www.wikiwhat.page/kavramlar/Evaporative%20Cooling

In summary, while freezing temperatures are required for snowflake formation, it can snow even if the surface temperature is slightly above 0°C. The atmospheric temperature profile, presence of melting layers, and humidity all play significant roles.