[colloydi]

Tangential to the topic but regarding the supposed Snowball Effect there is in real life no such thing. I have pushed large 'snowballs' down slopes --in reality they are snow cylinders as shown in the photo-- and they invariably do not get far. The reason being that when one side of the cylinder randomly thickens slightly with respect to the other side this causes the whole thing to turn in the opposite direction.

For example, if the RHS of your cylinder has a slightly larger radius than the LHS the cylinder will commence turning to the left.

The upshot is the thick side picks up more snow than the thin side and the disparity in radii increases more rapidly still. The cylinder becomes a truncated cone which turns sideways and halts!

[lsowen]

It might be rare, but it _can_ happen: https://www.youtube.com/watch?v=ZdIclqha014

[dendrite9]

It is highly dependent on the snow conditions and the recent weather. Sometimes even just the a couple hours are enough to change the conditions to have a good chance of rollerballs. The climate also has an impact, in my experience more coastal areas have more periods when they form.

And in some cases the rollerballs get too tall for the bonding strength of the snow, so they break into parts that can restart the cycle if the slope is steep enough.

[whinvik]

Sounds to me like there's a long blog post waiting to be written.