Snow rollers are formed when the wind blows wet snow into a roll. There needs to be enough light fluffy snow, the temperature has to rise above freezing to make the snow sticky and a strong enough wind is required to roll the snow in layers.
Psalm But his delight is on the law of the Lord, and on his law he meditates day and night. He is like a tree planted by streams of water, which yields its fruit in season and whose leaf does not wither. Whatever he does prospers.