Hoarfrost formation in a maritime inversion climate has been studied via inferred snow/air interface temperatures, vertical temperature profiles of the interface, and application of dew point hygrometry. Two dominant growth situations have been discerned. The first involved highly saturated air near the interface and strong radiational cooling of the snow surface, producing a wide variety of crystal sizes (1- 6mm). The second showed strong radiational cooling of the snow surface in an undersaturated environment with secondary introduction of water vapor from the presence of supercooled clouds. The latter often showed accelerated growth, the formation of large dendritic crystals (8-15mm) in short time periods (less than four hours).
Subsequent snowfalls of increasing water equivalent on surface hoar beds resulted in numerous direct action avalanches. Threshold crystal size for bed layer weakness varied widely (0.7-15mm) and was related to old snow surface roughness and new snow precipitation characteristics.