Winter Precipitation Explained: How to Identify, Prepare For, and Survive Mixed Ice Storms

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Casual observers often lump all frozen moisture together, yet sleet, graupel, and freezing rain possess fundamentally distinct microphysical origins. Sleet consists of ice pellets that started as snow, melted into rain within an elevated warm layer, and completely refroze before hitting the ground. When sleet hits a windshield or storm door, it produces a distinct pinging sound and bounces without coating surfaces in seamless ice.

[ Upper Atmosphere: Below Freezing (Snow Forms) ]

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[ Warm Inversion Layer: Above Freezing (Snow Melts to Rain) ]

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[ Deep Surface Cold Layer ] [ Shallow Cold Layer (<2,000 ft) ]

Pellets refreeze in flight Drops supercool; freeze on contact

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[ SLEET ] [ FREEZING RAIN ]

(Bounces, gravel-like) (Clear glaze, structural damage)

Graupel, often labeled soft hail or snow pellets, follows a different trajectory altogether. Graupel forms inside convective winter clouds where supercooled water droplets collide with and freeze onto the outer surfaces of falling snowflakes. This process, called riming, encases the snowflake in a soft, opaque crust of rime ice. Graupel pellets are typically milky white, crush easily between two fingers, and disintegrate upon impact rather than bouncing like dense sleet.

Freezing rain represents the most treacherous phase of this winter continuum. Because the surface cold pool is too shallow to trigger mid-air refreezing, the falling water drops remain liquid at temperatures below 32°F. The moment these supercooled droplets strike an unheated surface, a highway deck, an aluminum ladder, or an evergreen bough, their surface tension breaks, creating an immediate, uniform veneer of clear glaze ice.