Machine snow comes out wet when droplets cannot fully freeze before they land — almost always because the wet-bulb temperature is too high, and high humidity is the usual culprit. A droplet that reaches the ground half-frozen arrives as a heavy, water-laden clump instead of a dry crystal, and once it refreezes it glazes into an icy, hard-to-groom surface. The fix is to lower the effective wet-bulb, improve nucleation, or wait for a colder window.
If your snow is skiing wet, heavy, or icy, it is a diagnostic, not just a nuisance. It tells you exactly which variable is out of range. This guide explains why it happens, how to read your own snow, and the levers — operational and chemical — that recover a drier, more groomable surface in marginal conditions.
Key takeaways
- Wet machine snow means incomplete freezing in flight — the droplets did not lose enough heat before landing.
- The controlling variable is wet-bulb temperature, not air temperature; at high humidity, snow can be poor even below 0 °C air temperature.
- Humidity is the quiet killer: it raises the wet-bulb toward the air temperature and starves droplets of evaporative cooling.
- Practical fixes: make snow in the coldest hours, cut water flow per gun, improve air/water mix and nucleation, and site guns for maximum droplet hang-time.
- A polymer additive addresses the same root cause — better nucleation plus recrystallization inhibition — to recover drier snow in the marginal wet-bulb window (a modelled benefit).
Why does machine-made snow come out wet?
Because each water droplet has only a fraction of a second in the air to freeze, and if it cannot shed enough heat in that time, it lands still partly liquid. Snowmaking works by throwing atomised water into cold air so each droplet freezes in flight. When conditions do not pull heat out of the droplet fast enough, freezing is incomplete and the "snow" arrives wet, dense, and clumped.
The heat leaves a droplet two ways: by conduction into cold air, and — critically — by evaporation from the droplet surface. Evaporative cooling is the larger effect and the one humidity controls. In dry air, water evaporates off each droplet fast, cooling it well below the air temperature; in humid air, evaporation nearly stops, and the droplet only cools to something close to the air temperature. That single mechanism is why two nights at the same thermometer reading can produce completely different snow. The physics of how droplets seed ice is covered in ice nucleation in snowmaking.
There is also a quality dimension beyond wet-versus-dry. Even snow that freezes will coarsen after it lands, through Ostwald ripening — and coarsening is what turns a soft surface hard. Wet snow that then refreezes coarsens fastest of all, which is why marginal-temperature snow so often ends up as boilerplate.
Why is wet-bulb temperature the number that matters, not air temperature?
Because wet-bulb temperature already accounts for humidity, and humidity decides how much a droplet actually cools. Wet-bulb temperature is the lowest temperature you can reach by evaporating water into the air — exactly the process happening on the surface of every snowmaking droplet. It is the true "can I make snow" reading, and it is always at or below the air temperature.
The gap between the two is set by humidity, and it is large enough to flip a night from productive to hopeless:
| Air temperature | Relative humidity | Approx. wet-bulb | Snowmaking outlook | |---|---|---|---| | −2 °C | 30% | ~ −5 °C | Good, dry snow | | −2 °C | 90% | ~ −2.5 °C | Marginal, wet snow | | 0 °C | 30% | ~ −3 °C | Marginal but workable | | 0 °C | 90% | ~ −0.5 °C | Very poor / not viable | | +1 °C | 40% | ~ −1.5 °C | Marginal, additive territory |
Approximate values for illustration; use a psychrometric chart or your automation's wet-bulb readout for operational decisions.
The table shows why a night at 0 °C can be excellent or unworkable depending only on humidity — and why the "warm" complaint about wet snow is usually really a humidity complaint. Reading and using the wet-bulb properly is the highest-leverage skill in the pump house; the full operator's treatment is in the wet-bulb temperature guide.
How do I fix wet snow tonight?
Attack the wet-bulb and the freezing time directly. None of these change the weather, but together they can pull a marginal night back toward dry snow. Work through them in order of speed:
- Shift to the coldest, driest hours — usually pre-dawn, when both temperature and humidity drop. A few hours of patience often beats fighting a warm evening.
- Cut water flow per gun. Fewer, smaller droplets freeze more completely. Overwatering is the most common self-inflicted cause of wet snow at the margin.
- Improve the air/water mix and nucleation. More nucleation seeds and better atomisation give each droplet a faster, more reliable freeze.
- Move air where you can. Fan guns and good siting extend droplet hang-time; a longer flight is more freezing time.
- Prioritise terrain. Put the marginal-window output where it protects open days — connectors, race trails, the early-season base.
These are the same efficiency levers that drive down cost per m³ of snow, which is why quality and economics move together; the cost side is in how to reduce snowmaking costs and the quality-management side in snow quality control.
Does wet snow cost a resort more than dry snow?
Yes — twice over. Wet snow wastes energy and water making a poorer product, and it forces rework when the surface glazes or fails to hold. Snowmaking is already a heavy line item: about 17% of daily operating cost at large Swiss resorts (Vorkauf et al. 2022), and in absolute terms Austria's snowmaking runs to roughly 281 GWh of electricity and 51 million m³ of water per season (Aigner, Steiger & Mayer 2026). Every hour spent overwatering in a marginal window spends that energy and water for snow you may have to remake.
The waste has two forms. Directly, water pumped as unfrozen droplets is water and pumping energy that produced no usable snow. Indirectly, a wet layer that refreezes into ice often has to be groomed harder, tilled, or covered over — labour and machine hours on top of the original spend. Because wet snow also coarsens faster once it refreezes, it degrades sooner, shortening the return on the snow you did manage to bank. Reading the wet-bulb correctly and cutting flow at the margin is therefore a cost decision as much as a quality one.
Where does a snowmaking additive fit?
It targets the exact failure mode — incomplete freezing — by improving nucleation, and it protects the result by slowing recrystallization. An additive does not warm or dry the air. What it does is help each droplet freeze more completely in the same short flight, and help the finished crystals hold their structure instead of coarsening into ice. In effect, it lets a resort make cold-night-quality snow at a higher wet-bulb than it otherwise could.
Two components do the work in SL6733: a cold-water-swelling starch nucleant that seeds freezing, and an anionic polymer that delivers ice recrystallization inhibition to keep grain size down after landing. The modelled result is a wet-bulb advantage of about +3 °C — meaningful hours recovered at the warm edge of the season, described in making snow at warmer temperatures. It is dosed at parts-per-million and works with any snow gun, so it is a process aid layered on top of the operational fixes above, not a replacement for them.
The honest framing is that the additive extends the window, not the laws of physics. Above a certain wet-bulb, no chemistry makes snow; below it, the additive buys back quality and hours that warm, humid conditions would otherwise cost. Those recovered hours are what convert into open days, as covered in extending the ski season.
The bottom line
Wet machine snow is a freezing problem, and the number that governs it is wet-bulb temperature — driven far more by humidity than by the thermometer. Read the wet-bulb, make snow in the coldest and driest hours, cut overwatering, and get nucleation and droplet hang-time right, and most "warm" nights improve. Where operational levers run out at the margin, better nucleation and recrystallization inhibition — the job of a polymer additive — recover a slice of the dry, groomable snow the weather is trying to take away.
If you want to quantify how many marginal hours you are losing and what recovering them is worth, request a pilot or send us a message.
Wet-bulb figures above are approximate and for illustration; use your own instrumentation for operational decisions. SL6733 outcomes, including the +3 °C wet-bulb advantage, are modelled and the additive is pre-commercial. DeepSnow is the platform brand of SnowLabs Limited (Ireland); DeepSnow Srl (Italy) is in formation.