Thursday, February 14, 2013

Baby Graupel

The area around campus was littered this morning with small, spongy, ball-shaped snow pellets that fell over night.  They are indeed fully recyclable.

Most clouds are comprised of a mixture of ice crystals and supercooled cloud droplets.  Supercooled means that the droplets are below freezing, but remain in the liquid phase.  Graupel is a type of snow pellet that forms as an ice crystal falls and collects these supercooled cloud droplets, which freeze on contact.  This leads to the formation of a ball or lump shaped snow pellet.

Source: Parkerjh, Wikipedia Commons
The snow pellets that fell last night were, however, quite small.  I don't know if there is a minimum size requirement for graupel, so I'll call them "baby graupel."  The formation mechanism was probably similar to that of graupel.  Small ice crystals collected supercooled cloud droplets as they fell.  They just didn't grow to a large size. 


  1. What was up with the PM2.5 bump last night/this morning?

    My theory is that we had moderately bad air, the stuff over the lake was worse, and it got pushed by Hawthorne with this little storm?

    1. Thanks for the heads up. I just looked at the PM2.5 time series and it did exhibit some strange behavior. The flow did switch from SW to NW as the trough came through. What is odd is how it dropped around noon. Perhaps there was a some gunky air over the lake, it got swept in with the trough, but eventually cleaner air replaced it? It's tough to say given the lack of AQ data upstream.

  2. Jim,

    Looks like low-density and nearly round pellets - so I'd tend to call then snow pellets. I don't know if there's a density criteria for graupel, which tends to be more dense than snow pellets because of its faster growth rate. Just my guess.