What is Graupel?

(Photo: Merlot)

 

 

When I walked outside early this morning (about 7:30), it looked like someone had been very busy with a fertilizer spreader!  There were little white pellets or balls all over the ground. If you picked one up, it was not icy, but like a tiny little snowball, soft and easily flattened out. They melted pretty fast, too.

 

Someone on a weather FB page had a comment about these little white pellets that were everywhere and their home was in Chesterfield so it appears this was a fairly widespread occurrence.  A possible name and link was given ..... it appears this is called Graupel and also known as 'soft hail' or 'snow pellets'.

 

From Wikipedia :

 

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 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. 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.

 

Graupel commonly forms in high altitude climates and is both denser and more granular than ordinary snow, due to its rimed exterior. Macroscopically, graupel resembles small beads of polystyrene. The combination of density and low viscosity makes fresh layers of graupel unstable on slopes, and layers of 20–30 cm (7.9–12 in) present a high risk of dangerous slab avalanches. In addition, thinner layers of graupel falling at low temperatures can act as ball bearings below subsequent falls of more naturally stable snow, rendering them also liable to avalanche. Graupel tends to compact and stabilise ("weld") approximately one or two days after falling, depending on the temperature and the properties of the graupel.

 

 

I learned something today ...... and the next time I see little white balls all over the yard or in the woods, I'll know what they are! ~ Merlot