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Graupel

timv's picture

Strange weather today: Cold and rainy in the morning, clear and sunny in mid-afternoon, and then a dark and mean-looking line of clouds rolled in just after 5 pm as I was walking across campus. I would have thought a thunderstorm was coming in the summer, but didn't know whether to expect rain or snow this time of year and in this particular (and peculiar) year. We got neither of those:

(Cribbed without shame from Wikipedia.)

Graupel. Not to be confused with Hail or Ice pellets.

Graupel (also called small hail, soft hail, or snow pellets) refers to precipitation that forms when supercooled droplets of water condense on a snowflake, forming a 2–5 mm ball of rime; the snowflake acts as a nucleus of condensation in this process. Graupel is the German word for this meteorological phenomenon.

Under some atmospheric conditions, snow crystals may encounter supercooled cloud droplets. These droplets, which have a diameter of about 10 µm, can exist in the liquid state at temperatures as low as −40 °, 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 is both denser and more granular than ordinary snow, due to its rimed exterior. Macroscopically, graupel resembles small beads of polystyrene.

Location

1601 East Market Street
Greensboro, North Carolina 27401
United States
36° 4' 18.6564" N, 79° 46' 40.6236" W

Comments

eebee's picture

Yesterday's Radar, Telling Yesterday's Weather

How cool, Timv. This is something I had read about in all my weather books and now looking at a picture of it, remember seeing it. I think I filed it away in my brain as 'that polystyrene-like snow'.

Here's a site for yesterday's radar, which I have needed for past skate event write-ups but not found. Looks like there was plenty of ice in that line.

Graupe is German for hulled grain or groats, so I guess hence the description for this type of precip. I knew hail as Hagel in German, but my old trusty Cassell's dictionary lists both.

timv's picture

groats

As least you had heard of it and seen it before. I had done neither and had no idea what it was until I got home. All of the local weather personalities were in nerd glory having something new like this to talk about.

It came down hard but wasn't nearly as bad as getting caught in hail or sleet. It was like a Nerf version of sleet. Or maybe like being shot-blasted with puffed rice.

Oh well, I can't cross anything off my bucket list but I don't have to add that to it either.

Nice find for yesterday's radar. That could be handy.

eebee's picture

Glorified Nerds

Talking of which, I notice ex-TWC heart throb Jim Cantore has busted through to the big time and is now presenting NBC's winter Olympics weather...or lack thereof. 

It must've been a substantial amount to have made the local news! I'm hoping spring is going to be equally exciting. I believe it has been another El Nino winter, which usually makes the jet streams do unusual things, bringing unusual weather, and often tornadic springs in the South. 

"...like being shot-blasted with puffed rice." Now there's a useful application for rice cakes! That might catch on for kids' birthday parties.

I had totally forgotten about this...but I now recall talking to Roadskater on the phone during that mini-storm and hearing him say 'We have snail here!'. He meant there was a mix of snow and hail falling. Why not?! I'm hearing the word gustnado more and more.

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