You may have heard someone declare, “It’s too cold to snow.” Is it true? Can it be too cold to snow? Technically, it’s never too cold to snow because water freezes at any temperature below its freezing point (and sometimes above it). However, there is a grain of truth to the notion because cold air is more stable than warm air and it holds less water.
Technically, it can’t be too cold too snow. However, it can be too dry, which indirectly results from low temperature.
Snowflakes form when tiny water droplets freeze into crystals around dust or pollen particles. This happens when three requirements are met:
- Water vapor: Clouds usually form when an air mass rises. Atmospheric pressure decreases with altitude, causing the air mass to expand, which makes it cooler and reduces the amount of water it can hold.
- Cold temperature: Sometimes the expansion of air is enough to cool it below the freezing point of water so ice crystals form. The crystals link together to form snowflakes Snowflakes are heavier than air, so they fall as precipitation. Snowflakes cool the air around them, so they last a while even if the surface temperature is above freezing.
- Unstable air: Air rises and forms clouds when there is instability or a pressure difference. In the mid-latitudes the air is almost always unstable enough to allow snow, due to topography, vegetation, surface water, and weather fronts. Even if the surface is very cold, the air aloft may be warmer, plus it can draw in additional moisture from the sides by advection.
What Temperature Is Too Cold?
Snowfall becomes unlikely in the mid-latitudes when temperatures drop below -20° C (-10° F). When it’s this cold, water vapor forms ice crystals, but they don’t necessarily form flakes for two reasons. Very cold air holds so little water, the crystals are further apart and tend to settle out rather than link together to form snowflakes. Also, temperature affects the shape of ice crystals. Water forms needle-like shapes when it’s well below freezing, not flat hexagons or branched flakes.
Where It’s Too Cold to Snow
In the winter in certain parts of Antarctica, temperatures hover at -40° C (or -40° F) or cold for a long time. There isn’t enough of a temperature difference between the surface and the air column for air to pick up water and deposit precipitation. While the continent has geographical features, the lack of interior water or vegetation makes the air column highly stable. Sometimes ice crystals and ice fog form, but neither of these is considered to be “snow.”
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