John Wheeler: Freezing rain and freezing drizzle are very different processes

FARGO — Freezing rain and freezing drizzle, both terrible hazards to travelers, happen several times each winter, but are often hard to forecast. Freezing rain happens when snow falls through a warm layer of air near the ground, which melts the snow into rain, and the rain then freezes on impact with a frozen ground. Freezing drizzle is made of much smaller droplets and often is not associated with a warm layer.

Freezing drizzle often forms in clouds where the temperature is below freezing. Snowflakes in a cloud grow onto pieces of dust or small ice crystals, and in very specific cases, especially when the cloud top temperatures are between 10 and 18 degrees and the air is very dry above the cloud layer, moisture droplets will remain liquid at temperatures well below freezing. So instead of snow, the cloud produces small droplets of “super cooled” water, which instantly freeze on contact with any surface.



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