Producing artificial snow is a technological necessity for ski resorts aiming to extend seasons and guarantee adequate coverage. This process involves converting water into ice crystals by spraying fine droplets into cold air. Determining the necessary atmospheric conditions for this conversion is not as straightforward as checking a standard outdoor thermometer, as the required temperature depends on more than just the air reading alone.
Why Air Temperature Alone Is Misleading
The temperature that truly governs successful snowmaking is known as the wet bulb temperature (WBT), which combines the ambient air temperature and the relative humidity. This single metric is a more accurate measure of the atmosphere’s capacity to cool the water droplets sufficiently for freezing. The WBT is always equal to or lower than the standard air temperature, except in conditions of 100% humidity. Snowmaking relies heavily on evaporative cooling, where some water evaporates, drawing heat away from the remaining liquid droplets.
When the air is dry, evaporation occurs rapidly, which pulls more heat from the water, resulting in a lower WBT and a more efficient freezing process. Conversely, if the air holds a high amount of moisture, evaporation slows down significantly, retaining heat and making it difficult for the water to freeze. For example, snow can sometimes be made even when the air temperature is slightly above the freezing point of water, provided the humidity is very low. This means a night of 30°F with low humidity might be better for production than a 27°F night with high humidity.
The Physics Behind Artificial Snow
Artificial snow is created by specialized machines, often called snow guns, that atomize water and project it into the cold air under high pressure. Atomization is the mechanical process where water is broken down into a fine mist of tiny droplets, typically ranging from 100 to 700 microns in diameter. This fine mist increases the total surface area of the water, which maximizes the effect of evaporative cooling as the droplets travel through the air. The physical goal of the machine is to ensure the droplets freeze before they fall to the ground.
Nucleation
These machines also require a component called a nucleator, which is responsible for creating microscopic ice crystals. Water droplets alone often require extremely low temperatures to freeze spontaneously, a phenomenon called supercooling. Nucleators use compressed air and a small amount of water to produce tiny ice seeds that serve as a structure for the supercooled water droplets to freeze around. These ice seeds are mixed with the atomized water stream, initiating the crystallization process at much higher temperatures. The resulting plume of seeded water droplets then continues to cool through evaporation as it falls, transforming into machine-made snow.
Practical Temperature Thresholds for Production
The industry generally uses the wet bulb temperature (WBT) as the operational threshold for initiating and maintaining snow production. Marginal snowmaking conditions begin when the WBT drops to approximately 28°F (-2.2°C). At this temperature, production is possible, but the output is slow and the resulting snow tends to be wetter and slushier in texture. This is often the minimum condition required for modern equipment to operate effectively.
To achieve efficient production and higher quality snow, the WBT must be significantly colder. Optimal conditions for snowmaking begin around 20°F (-6.7°C) and below, where the rate of production increases dramatically. When the WBT reaches 15°F (-9.4°C) or lower, the machinery operates at peak efficiency, producing a large volume of drier, more desirable snow. The colder the WBT, the faster the water freezes, allowing snowmakers to convert more water into snow quickly and build a deeper base.