The question of how fast a snowflake falls does not have a single, fixed answer because the term “snowflake” describes a vast collection of unique structures. A snowflake is an aggregate of many individual ice crystals that have collided and bonded together as they descend through the atmosphere. The speed of its descent is a highly variable measurement, changing moment by moment for every piece of frozen precipitation. The movement of these particles is often more of a gentle drift than a direct fall, which highlights the complexity behind determining their true vertical velocity.
The Typical Speed of a Snowflake
The downward speed of a falling object eventually reaches a constant maximum velocity known as terminal velocity. This occurs when the force of air resistance, or drag, perfectly balances the downward pull of gravity. For a snowflake, this balance is achieved quickly due to its low mass and relatively large surface area.
The typical vertical speed for a snowflake falls within a range of about 1 to 6 miles per hour (0.3 to 2.7 meters per second). This low terminal velocity is why snow often appears to float lazily. The exact speed depends on the snowflake’s physical characteristics and the immediate atmospheric conditions.
Physical Factors That Determine Fall Rate
The considerable variation in a snowflake’s fall rate is determined by its mass and its interaction with the surrounding air. The two most influential physical factors are the mass and aggregation of the crystal, and its overall shape, which dictates air resistance. Larger, heavier snowflakes tend to fall faster because the gravitational force acting on them is greater than the opposing drag force they experience.
Mass and Aggregation
Aggregation, the process where multiple ice crystals stick together to form a larger clump, increases the total mass without a proportional increase in surface area, thus increasing the speed. This mass-to-surface area ratio is altered by riming, where supercooled water droplets freeze directly onto the snowflake, increasing its density and weight. This denser, heavier structure falls at a higher terminal velocity compared to its unrimed counterparts.
Shape and Drag
The second primary factor is the snowflake’s unique shape and the resulting air resistance, or drag. Complex, highly branched crystal types, such as stellated dendrites, have an intricate, lacy structure with a large surface area for their mass. This structure creates greater drag, which acts to slow the snowflake’s descent considerably. Conversely, smaller, more compact ice pellets or plates have less surface area relative to their weight, allowing them to slice through the air with less resistance and fall more quickly.
Snowfall Compared to Other Precipitation
A snowflake’s gentle rate of descent becomes clear when compared to other common forms of precipitation.
Rain
Liquid raindrops fall significantly faster than snow due to their higher density and more compact, spherical shape, which minimizes air resistance. A typical large raindrop can reach terminal velocities around 15 to 20 miles per hour (7 to 9 meters per second). This speed is many times greater than the speed of a snowflake.
Hail
Hail, which is composed of dense layers of ice, exhibits the highest fall speeds among common precipitation types. Hailstones are extremely dense and heavy, leading to a much higher mass-to-surface area ratio than either rain or snow. Large hailstones, driven by powerful storm updrafts, can reach speeds exceeding 90 miles per hour before they hit the ground.