Supercooled Warm-Rain Processes: the formation of freezing rain

A less common way that freezing rain forms is through supercooled warm-rain process (SWRP), where cloud top temperatures are warmer than about -10C. Supercooled raindrops develop as microscopic cloud droplets collect one another as they fall. Ice processes are not involved in the formation of these raindrops.

[Image: All supercool raindrops (22K)]

The precipitation falls to the surface as supercooled rain or drizzle and freezes instantly on contact. The raindrops do not freeze within the cold layer because there are very few ice nuclei in the presence of warmer temperatures.

[Image: Freezing rain on a tree (30K)]
Photograph by: Olthoff

The freezing rain forms a coat of ice on everything. This picture shows several tree branches coated with a thick layer of ice that accumulated during a central Illinois ice storm.

ice-crystal

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Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

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