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.

original latin

Beda affert et confirmat, cuius ratio est, quia maris fumositates continuae vel exhalantur, vel a ventis ibidem flantibus disperguntur, vel antequam possint condensari in nivem, in pluviam vel nebulam resolvuntur.

Item, feris et animalibus nocumentum praestat, quia eorum tegit pascua, et vestigia manifestat, unde tempore nivis ferae a venatoribus de facili capiuntur.

Item, loca alta et montuosa nix frequentat, et diutius in montibus quam in vallibus perseverat, quia venti frigidi liberius in montibus quam in vallibus invalescunt. Insuper valles sunt montibus calidiores propter maiorem aggregationem et confractionem radiorum, et ideo nives in montibus plus abundant.

Item, nix vi caloris resoluta terram imbuit, remollit et inebriat, quam ante resolutionem frigiditatis suae coarctatione in sua superficie fortius indurabat, ut dicit Gregorius.

Item, nix propter suae substantiae mollitiem et levitatem in suo descensu strepitum vel sonum non generat, immo sensibiliter de occulto aeris descendens interstitio suaviter superficiei terrae se applicat, et aequaliter se coaptat.

Item, nix in candore suo et pulchritudine ad sui aspectum oculos intuentium provocat, sed si nimis diu aspiciatur spiritum visibilem disgregat et valde immutat.