The seemingly gentle descent of snow often leads people to wonder about its actual speed. Unlike a raindrop that streaks quickly toward the ground, snow appears to float and drift, suggesting a much slower rate of fall. The physics behind this movement dictates a wide range of speeds for this type of precipitation. The speed at which snow falls is typically found between 1 and 6 feet per second.
Understanding Terminal Velocity
The fall speed of a snowflake is governed by terminal velocity. This is the maximum speed an object can reach while falling through a fluid, such as air. Terminal velocity occurs when the downward force of gravity is perfectly balanced by the upward force of air resistance, or drag, causing the object to stop accelerating and fall at a constant rate.
The range of 1 to 6 feet per second (0.3 to 1.8 meters per second) indicates the variability in this balance of forces. For any falling object, the greater the surface area relative to its mass, the higher the air resistance, which results in a lower terminal velocity. This principle explains why a flat sheet of paper falls slowly compared to the same paper crumpled into a tight ball.
Variables That Govern Snowflake Speed
The wide speed range of falling snow is primarily due to the vast array of shapes and sizes that snowflakes can take. The geometry of the ice crystal is the most significant factor determining the air resistance it encounters.
A snowflake with an intricate, dendritic, or star-like shape presents a much larger surface area to the air, acting like a parachute to slow its descent. Conversely, more compact forms, such as plate-like or columnar crystals, have a smaller surface area relative to their mass, allowing them to fall at the faster end of the speed range.
Aggregation also plays a role, as multiple ice crystals clump together to form a large snowflake. While this clumping increases the particle’s mass, it also drastically increases its size and surface area. This often results in a lower terminal velocity compared to a dense, individual pellet of ice.
Influence of Atmospheric Conditions
Atmospheric conditions like air density and temperature also influence the fall rate. Lower air density, found at higher altitudes, provides less resistance, allowing for a slightly faster fall. However, the influence of the snowflake’s structure—its shape and density—far outweighs the effect of changes in air composition near the ground.
How Snowfall Speed Compares to Other Precipitation
When the speed of snow is compared to other forms of precipitation, its slow descent becomes apparent. The terminal velocity of a typical snowflake, at 1 to 6 feet per second, is far less than that of a common raindrop. Raindrops are much denser and more streamlined than snowflakes, allowing them to reach speeds ranging from 10 to 30 feet per second.
The difference is due to the high surface area-to-mass ratio of snow, which provides substantial drag. This contrasts sharply with denser precipitation types.
Denser Precipitation Types
Graupel, often called soft hail or snow pellets, is formed when supercooled water droplets freeze onto a snowflake. This creates a dense, opaque pellet that falls much faster than a typical snowflake.
Hail, composed of layers of solid ice, is the fastest of all because its mass is far greater relative to its surface area. Small hailstones can fall at speeds of 40 miles per hour, and large hailstones can exceed 100 miles per hour.