Final answer:
The correct answer is hoar frost, which forms from direct sublimation of water vapor in the air on cold, clear nights when objects are cooler than the dew point.
Step-by-step explanation:
The type of weak snow layer formed as frozen dew deposition when air temperature is warm and snowpack is cold with little wind is known as hoar frost. This occurs because significant heat is required for phase changes. Snow, being the solid phase of water formed from ice crystals, requires time for the necessary heat to be transferred from the air—even if the air is above 0°C. Hoar frost is essentially a deposit of ice crystals formed by the direct sublimation of water vapor from the air. It typically happens on cold, clear nights when objects cool to a temperature lower than the air's dew point.