Field observations of surface hoar formation were carried out with the measurements of water vapor condensation rate, snow surface temperature, air temperature, humidity, wind speed, and net radiation. Large surface hoar crystals were observed to form under the breezy wind, 1 to 2 m s-1, at 0.1 m high. The condensation rate increased linearly with the product of the vapor pressure gradient and the wind speed. The bulk transfer coefficient of water vapor Ce was roughly constant when the surface hoar crystals were small, whereas it showed some increase as the hoar crystals grew to several millimeters in height. A possible cause of this increase in Ce is that the developed surface hoar crystals modify the aerodynamic roughness and consequently increase the turbulent transfer of water vapor.¿ 1997 American Geophysical Union