Compacted snow

[237SJ]

Sometimes when it snows, the snow falls as little compacted balls. It`s not hail, freezing rain or snow flakes. What causes this?

[Clanad]

Depending on conditions, they're either Snow Grains or Snow Pellets.... Snow grains are simply frozen drizzle, while snow pellets are "... White, opaque ice particles that form as ice crystals fall through cloud droplets that are below freezing but still liquid (supercooled). The cloud droplets freeze to the crystals forming a lumpy mass. Scientists call snow pellets "graupel." Such pellets falling from thunderstorms are often called "soft hail." )Source: "Weather for Aviators").

As an aside, having been a commercial pilot all my adult life, one of the worst aircraft iding conditions one can encounter is associated with snow pellets since the super cooled water droplets strike the leading edges of any aircraft flying through it, but doesn't freeze for a very short period of time. It then trails in the slipstream back over the wing until it does freeze. Back in the day when most aircraft's wings were deiced by an inflatable "boot" attached to the leading edges of the wings and tail, the supercooled moisture would eventually form a dam just aft of the deice boots causing much untold disconcerting inspection of the wings by the crew... even to the point of (on some aircraft) having the first officer (copilot) coming back into the cabin to more closely view the wings through the passenger windows.
With the advent of haeted leading edges, the problem was somewhat lessened and with th eproliferation of jets, flight in the weather phenomena was eliminated by the aircraft's ability to climb swiftly through it. Still a concern on approach and landing phases of flight however...

[237SJ]

Thanks Clanad. I`m `in the business` too (self loading freight)! I`m off to Hong Kong later and it`s freezing here. I`m hoping we don`t wait ages for de-icing and get horrendously delayed. I don`t think there`ll be any compacted snow over Kowloon any time soon!