TL;DR. Wet-bulb temperature, not dry-bulb, sets the operational ceiling for snowmaking. Most resorts can produce reliable snow at a wet-bulb of about −2 °C; below that, snowmaking becomes intermittent or stops. Every additional 1 °C of wet-bulb headroom unlocks ~100–200 additional snowmaking hours per season for an average alpine resort. SL6733 is engineered for a +3 °C wet-bulb advantage. This guide explains the physics, the operational math, and what changes when climate warms.
What wet-bulb actually is
When you spray a fine droplet of water into cold dry air, it does not immediately reach the air temperature. It evaporates from its own surface as it falls. Evaporation removes latent heat. The droplet cools below the air temperature.
The lowest temperature a droplet can reach through this evaporative cooling is the wet-bulb temperature of the air it is moving through. It depends on two variables:
- Dry-bulb temperature (the air temperature your thermometer reads)
- Relative humidity (how much water vapor the air already contains)
At 0% humidity, the wet-bulb is much lower than the dry-bulb — evaporation is maximally effective. At 100% humidity, the wet-bulb equals the dry-bulb — no evaporation possible.
For snowmaking, the wet-bulb is the temperature the water droplet actually reaches as it falls toward the snowpack. If the wet-bulb is below freezing, the droplet can freeze before it lands. If the wet-bulb is above freezing, it cannot — no matter how cold the dry-bulb is.
A practical table
Approximate wet-bulb temperatures for typical alpine snowmaking conditions:
| Dry-bulb | 30% humidity | 50% humidity | 70% humidity | 90% humidity | |---|---|---|---|---| | 0 °C | −5.2 °C | −3.5 °C | −2.1 °C | −0.9 °C | | −2 °C | −6.5 °C | −5.0 °C | −3.7 °C | −2.6 °C | | −5 °C | −8.7 °C | −7.4 °C | −6.3 °C | −5.3 °C |
This is why humidity matters as much as temperature for snowmaking operators. A foggy night at 0 °C dry-bulb is essentially unusable. A clear night at 0 °C with 30% humidity is fully operational at −5.2 °C wet-bulb.
The operating ceiling
For conventional snowmaking (no additives), the operating ceiling is roughly a wet-bulb of −2 °C. Below that, you get reliable production. Between −2 °C and −1 °C, production is marginal — possible with effort, but yields are poor and snow quality degrades. Above −1 °C wet-bulb, conventional snowmaking effectively stops.
The reason is freezing kinetics. The droplet has a fixed time of flight between leaving the snowgun and landing. To freeze in that window, the wet-bulb has to be cold enough that the latent heat of fusion can dissipate before impact. Above −2 °C wet-bulb, the math does not work — most droplets land as slush or water.
Why an additive changes this
An effective snowmaking additive raises the wet-bulb ceiling. Two mechanisms are at play:
- Nucleation enhancement — the additive provides ice-active sites in the water that lower the energy barrier to crystal formation. Crystals nucleate earlier in the droplet's flight, giving more time for freezing.
- IRI — once formed, the crystals are kept small and dense (rather than coarsening), producing snow that holds up at marginal conditions.
SL6733 is engineered for both. The targeted wet-bulb advantage is +3 °C — i.e., the operator can produce reliable snow at wet-bulbs up to roughly +1 °C, instead of −2 °C.
What +3 °C is worth
For a typical mid-sized European alpine resort, climate data shows the average season distribution looks something like:
- ~1,200 hours per season at wet-bulb below −5 °C (fully usable today)
- ~600 hours per season between −5 °C and −2 °C (fully usable today)
- ~400 hours per season between −2 °C and +1 °C (lost today; recovered with SL6733)
- ~300 hours between +1 °C and +3 °C (still lost — SL6733's ceiling is below this)
- The remainder above the operational window for any chemistry
The 300–500 hours figure cited by DeepSnow comes from this distribution: the resort recovers most of the −2 °C to +1 °C window. The exact number varies by site, altitude, and microclimate.
At a snowmaking economic value of roughly €5,000–8,000 per hour of productive snowmaking (a number that includes downstream effects on season length, lift-ticket sales, and ancillary spend), the recovered hours map to roughly €2–3M per resort per season. The widely-cited $2.4–2.8M EBITDA uplift falls inside that band.
The climate-change dimension
The IPCC's central scenario for European Alps warming through 2050 is roughly +2 °C to +4 °C in mean winter temperatures. The implications for snowmaking are stark:
- At +2 °C average warming, the marginal-condition band shifts toward operators. The hours currently between −5 °C and −2 °C wet-bulb (today's "easy" hours) move toward −3 °C and 0 °C — i.e., into the band where conventional snowmaking starts failing.
- At +4 °C average warming, ~98% of European resorts are at risk of seasonal viability per published studies.
The economic consequence: every resort that survives the next two decades has to extend its operating envelope. An additive that adds +3 °C of wet-bulb headroom is not a minor optimization — it is a climate-adaptation tool.
What to ask
For an operator evaluating wet-bulb claims from a vendor:
- What is the claimed wet-bulb advantage, in °C? A specific number, with test conditions disclosed.
- What are the test conditions? Lab pilot? Field trial? Modelled? Modelled is fine if the model is documented.
- What is the operator-relevant dose? ppm-based, predictable. "Per ton water treated" is hard to procure against.
- How does the additive interact with my existing snowgun system? Drop-in versus retrofit.
How to measure your own wet-bulb
Operators wanting to calibrate against their own climate data:
- Most modern weather stations report wet-bulb temperature directly, or you can derive it from dry-bulb and relative humidity using standard psychrometric equations. The simplest online calculator is fine for back-of-envelope work.
- Build a 5-minute resolution wet-bulb distribution for the past 3 seasons of your operating window. That gives you a defensible estimate of how many "marginal hours" your specific resort loses today — and would recover with a +3 °C additive.