Graupel

Snow pelletssmall hailsoft hail
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime.wikipedia
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Precipitation

rainfallhydrometeorannual precipitation
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime.
The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail.

Hail

hailstormhailstoneshailstone
Graupel is distinct from hail and ice pellets. Ice from hail is formed in hard, relatively uniform layers and usually falls only during thunderstorms.
Unlike other forms of water ice such as graupel, which is made of rime, and ice pellets, which are smaller and translucent, hailstones usually measure between and in diameter.

Snowflake

snowflakessnow flakeflakes
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime. Graupel forms fragile, oblong shapes and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets.
Snowflakes encapsulated in rime form balls known as graupel.

Ice pellets

sleetice pelletrefreezed snow
Graupel is distinct from hail and ice pellets. Graupel forms fragile, oblong shapes and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets.
Ice pellets are smaller than hailstones which form in thunderstorms rather than in winter, and are different from graupel ("soft hail") which is made of frosty white rime, and from a mixture of rain and snow which is a slushy liquid or semisolid.

Rime ice

rimehard rimeSoft rime
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime.
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.

Snow

snowfallsnow coverSnowfalls
Under some atmospheric conditions, snow crystals may encounter supercooled water droplets. Graupel commonly forms in high-altitude climates and is both denser and more granular than ordinary snow, due to its rimed exterior.

Accretion (meteorology)

accretion
This process of crystal growth is known as accretion.
The collection of these particles eventually forms snow or hail in clouds and depending on lower atmosphere temperatures may become rain, sleet, or graupel.

Rain and snow mixed

sleetmixed precipitationa mixture of rain and snow
Graupel forms fragile, oblong shapes and falls in place of typical snowflakes in wintry mix situations, often in concert with ice pellets.
Wintry showers is a somewhat informal meteorological term, used primarily in the United Kingdom, to refer to various mixtures of rain, graupel and snow.

Supercooling

supercooledsupercoolsupercooled water
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime. Under some atmospheric conditions, snow crystals may encounter supercooled water droplets.

METAR

SPECIaviation flight categoryaviation
The METAR code for graupel is GS.

Atmosphere

atmosphericatmospheresplanetary atmospheres
Under some atmospheric conditions, snow crystals may encounter supercooled water droplets.

Drop (liquid)

dropletdropletsdrop
Graupel (Enɡlish: ), also called soft hail or snow pellets, is precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming 2 - 5 mm balls of rime. Under some atmospheric conditions, snow crystals may encounter supercooled water droplets.

State of matter

states of matterstatephysical state
These droplets, which have a diameter of about 10 µm, can exist in the liquid state at temperatures as low as -40 °C, far below the normal freezing point.

Freezing

solidificationfrozenfreeze
These droplets, which have a diameter of about 10 µm, can exist in the liquid state at temperatures as low as -40 °C, far below the normal freezing point.

Thunderstorm

thunderstormssevere thunderstormelectrical storm
Ice from hail is formed in hard, relatively uniform layers and usually falls only during thunderstorms.

Optical microscope

light microscopeoptical microscopycompound microscope
The frozen droplets on the surface of rimed crystals are difficult to see, and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument.

Angular resolution

resolutionRayleigh criterionresolved
The frozen droplets on the surface of rimed crystals are difficult to see, and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument.

Depth of field

depth-of-fieldDOFselective focus
The frozen droplets on the surface of rimed crystals are difficult to see, and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument.

Scanning electron microscope

scanning electron microscopySEMScanning electron micrograph
However, observations of snow crystals with a low-temperature scanning electron microscope (LT-SEM) clearly show cloud droplets measuring up to 50 µm on the surface of the crystals.

Granularity

granularfine-grainedcoarse-grained
Graupel commonly forms in high-altitude climates and is both denser and more granular than ordinary snow, due to its rimed exterior.

Polystyrene

expanded polystyrenestyrofoampolystyrene foam
Macroscopically, graupel resembles small beads of polystyrene.

Avalanche

avalanchesavalanchingavalanche research
The combination of density and low viscosity makes fresh layers of graupel unstable on slopes, and layers of 20 - 30 cm present a high risk of dangerous slab avalanches.

Lightning

lightning boltlightning strikelightning strikes
At that place, the combination of temperature and rapid upward air movement produces a mixture of super-cooled cloud droplets (small water droplets below freezing), small ice crystals, and graupel (soft hail).

Thundersnow

Heavy snowfall, accompanied by lightning and thundersnowthunder
In addition to snow, graupel or hail may fall as well.