Bartholomew says: "Snow results from cold and humid vapor making an impression in the deepest reaches of the intervening air, when the vapor is frozen in the body of a cloud. It is moderately cold compared to frost, because of the admixture of heat in a part of it. This heat, enclosed inside its substance, and not immediately extinguished by the cold around it, rarefies and mitigates its substance, which gets colored white, because of the dominance of the cold. On account of the expansion and dispersion of the parts of the clouds, and on account of the cold diminished by the heat, it breaks into broad particles like broken earthenware because of the weakness of the breaking [force].
"As Aristotle says. [cf. Meteorology 1.12] snow is created in a cold cloud, though it is less cold than [the cloud] in which hail is frozen. The softness of snow testifies to this, because the heat mixed with the cloud prevents its parts from condensing and aggregating more tightly. Therefore snow is harder and dryer than water because of the compressing cold, whereas it is softer than hail because of the addition of heat in the belly of the cloud."