CHARLESTON, S.C. – (WCBD) – The National Weather Service (NWS) Charleston on Monday evening issued an explainer, following multiple reports of a strange mini-hail-like precipitation falling from the sky throughout the Lowcountry.
According to the NWS, Graupel is precipitation that forms as snow, “then is rimed in layers by supercooled liquid from updrafts into showers.”
It is essentially a snowflake covered in supercooled water.
It typically “occurs when the lower atmosphere is very unstable.”
For graupel to form, surface temperatures generally must be lower than 45 degrees. Cloud temperatures should be below 32 degrees for the most part, “with some portion colder than 15 degrees.”
Graupel is similar to hail, which is precipitation “cycled through a cloud’s updraft with layers of ice growing concentrically from the center.” However, the range of temperatures in which hail forms can vary widely.