graupel

[corvi]

Last night, we got our first frozen precipitation of the year, and it was graupel. Graupel is caused when a normal snowflake crystal falls through a region of supercooled water droplets: droplets that are way below freezing temperatures, but have remained liquid. If any of the supercooled water touches a snowflake, it instantly freezes onto the snowflake as a little lumpy drop. So as the snowflakes fall, they collect little ice bits until they're tiny round snowballs. It's different from hail - a solid ball of ice - because it's soft and fluffy. Sometimes called "soft hail."

I think I've seen it once before, but it's not terribly common here. On the other hand, cold temperatures aren't common here either; I don't know how common graupel is in regions that get snow more than once or twice a year.

Here are some photos of snowflakes, arranged from "nearly normal snowflake" to "totally spherical graupel snowball" based on how many water droplets glomped them on the way from the clouds to us. At least 90% of what I saw out there were little round snowballs with no obvious snowflake features left, but I enjoyed trying to reconstruct the process, so I was specifically looking for ones that still had hints of six-fold symmetry.




















(Shoutout to the Olympus Tough TG-5 pocket camera, which juli  gifted me because I ruin one camera a year by getting headbutted by a goat or wading into a stream to chase ducks. It was chosen for the "tough" attribute, but it's actually a surprisingly excellent camera - I've never had a camera you could photograph snowflakes with before!)
 
Graupel is a major avalanche cause, because it's basically a layer of ball bearings; they don't lie flat or get hooked on eachother like regular snowflakes. If you get snow on top of the ball bearings, it will very easily slide off down a mountain. Much like our car did this morning. We ... might be stuck here for a bit.

(We're fine, the car is fine, it was a very slow slide, ably controlled by juli .)

Comments

Yes ...

[ysabetwordsmith]

I've seen it before. I'm amused you know the name -- not many people do. :D

[elinox]

Huh, didn't know that's what that stuff was called. I've seen it, and we get it occasionally here in PA.

[ivy]

I was totally going to ask how you got those photos! Macro-zoom, apparently!

the things one learns...

[twoeleven]

it's apparently relatively common out here, but i'm not convinced forecasts or radar returns distinguish it from sleet.

in ground school, they didn't make any distinction between the two. so, i'd never known there was a differnce. maybe that's simply a practical matter: neither one is a particular hazard to aircraft, unlike freezing [rain|fog] and hail.

[kellan_the_tabby]

I'd heard of it, knew the name, but seeing the process in your pictures makes it Real Stuff for me. *delight*

[ivy]

My girlfriend (!) commented that her co-worker wrote this paper about conical graupel, which is apparently an important type in winter weather. Your last shot looks just like some of the included photos in the article!

[beaq]

Graupel is the traditional first October "hail" in my front yard, and often takes the form of an Apollo command module. I haven't seen much over the last couple of years.

https://slideplayer.com/slide/9187913/27/images/10/Dual-Polarimetric+Parameters.jpg