Graupel

Graupel (German pronunciation: [ˈɡʁaʊpəl]; Enɡlish: [ˈgɹaʊpəl]), also called soft hail or snow pellets,[1] is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2–5 mm (0.08–0.20 in) balls of rime. The term graupel comes from the German language.

Graupel is distinct from hail, small hail and ice pellets: the World Meteorological Organization defines small hail as snow pellets encapsulated by ice, a precipitation halfway between graupel and hail.[2] The METAR code for graupel is GS.

Formation

Falling graupel

Under some atmospheric conditions, snow crystals may encounter supercooled water droplets. These droplets, which have a diameter of about 10 μm (0.00039 in), can exist in the liquid state at temperatures as low as −40 °C (−40 °F), far below the normal freezing point. Contact between a snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystal. This process of crystal growth is known as accretion. Crystals that exhibit frozen droplets on their surfaces are often referred to as rimed. When this process continues so that the shape of the original snow crystal is no longer identifiable, the resulting crystal is referred to as graupel.[3] Graupel was formerly referred to by meteorologists as soft hail. However, graupel is easily distinguishable from hail in both the shape and strength of the pellet and the circumstances in which it falls. Ice from hail is formed in hard, relatively uniform layers and usually falls only during thunderstorms. Graupel forms fragile, oblong shapes and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets. Graupel is also fragile enough that it will typically fall apart when touched.[4]

Graupel pellets in morning, having fallen the previous day
Other Languages
العربية: برد دقيق
Bân-lâm-gú: Thó-lūn:Sàn
беларуская: Крупка (ападкі)
беларуская (тарашкевіца)‎: Крупка (надвор’е)
Deutsch: Graupel
español: Granos de hielo
Esperanto: Grajlo
فارسی: برف‌دانه
français: Neige roulée
ગુજરાતી: કાચા કરા
客家語/Hak-kâ-ngî:
한국어: 싸라기눈
हिन्दी: कच्चा ओला
hrvatski: Solika
Bahasa Indonesia: Graupel
italiano: Neve tonda
עברית: גראופל
lietuvių: Sniego kruopos
magyar: Hódara
Nederlands: Korrelhagel
日本語:
norsk: Graupel
norsk nynorsk: Sprøhagl
português: Graupel
română: Măzăriche
Simple English: Graupel
slovenščina: Sodra
српски / srpski: Крупа (падавина)
suomi: Lumirae
svenska: Trindsnö
татарча/tatarça: Рашкы
українська: Крупи (опади)
文言:
中文: