Hail and snow are distinct forms of icy precipitation. While both descend from clouds, their formation processes are fundamentally different, leading to varied appearances and impacts upon reaching the ground.
How They Form
Snow forms when water vapor in the atmosphere freezes directly into ice crystals. This process occurs in clouds where temperatures are at or below freezing throughout the cloud. These ice crystals grow through deposition, where water vapor transforms directly into ice. As they grow, these crystals may collect supercooled water droplets that freeze onto them (accretion) or combine with other ice crystals (aggregation), forming snowflakes that eventually become heavy enough to fall.
Hail develops within the vigorous updrafts of cumulonimbus, or thunderstorm, clouds. These clouds contain strong air currents that carry supercooled water droplets high into the atmosphere, where temperatures are below freezing. As these droplets are lifted, they freeze upon contact with ice particles, forming an initial hail embryo.
Once an embryo forms, it falls through the cloud, collecting more supercooled water that freezes onto its surface. Strong updrafts then lift the growing hailstone back into colder regions, where it accumulates more ice. This repeated ascent and descent allows the hailstone to grow in layers, similar to an onion, until it becomes too heavy for the updrafts to support, at which point it falls to the ground.
Key Differences and Effects
Snowflakes are soft, delicate, and often intricate crystalline structures. They are white and possess a fluffy texture, accumulating in significant depths. Hailstones, in contrast, are hard, dense pellets of ice, spherical or irregular in shape, and can appear opaque or translucent, sometimes revealing distinct layers when cut open.
Snowfall occurs when ground temperatures are at or near freezing, making it a common phenomenon during winter months. Hail can fall during warmer seasons, such as spring and summer, because its formation happens high within towering thunderstorm clouds where temperatures are always below freezing. Snow is small, delicate flakes. Hailstones can grow much larger, ranging from pea-sized to golf-ball-sized or even larger.
Snow’s impact is primarily its accumulation, which can disrupt travel and provide a layer of insulation for the ground and vegetation. While heavy snowfall can cause structural issues, individual flakes lack significant destructive force. Hail, due to its density and velocity, causes substantial damage. It can devastate agricultural crops, dent vehicles, and compromise the integrity of roofs and other outdoor structures. Snowfall is largely silent, whereas hailstones striking surfaces produce a distinct thudding or clattering sound.