Mother Nature sometimes creates snowballs that seem to have come from nowhere.
When snow density, moisture content, wind speed, precipitation temperature, air
temperature et cetera are exactly right, bits of snow will be rolled across the surface,
picking up more snow as it rolls. It's just like a person rolling a snowball to make a snowman.
These snowballs can reach a foot in diameter but most don't exceed 1/2 foot.
Their size is limited to the winds ability to keep it rolling.
Nontheless, when conditions permit, there can be tens of thousands of these balls littering the fields.