Hi, I’m Dylan.

Corn snow is an informal classification of snow that is granular in texture and formed by repeated cycles of melting and refreezing. Each night, the snow surface freezes into a hard crust. As the sun warms the slope the next day, the top layer softens into loose, round grains, roughly the size and texture of actual corn kernels.

This freeze-thaw process is called melt-freeze grain metamorphism. It transforms the chaotic crystal structure of old snow into uniform, spherical ice grains. When the surface thaws to just the right depth you get corn.

Why skiers chase corn

Corn snow is the best surface most skiers will ever ride. The soft, predictable granules grip edges evenly and forgive mistakes. Turns feel smooth and controlled, almost like skiing on tiny ball bearings. It’s the reward for waking up early and timing your run right.

The catch: the window is short. Too early and the surface is still icy. Too late and it turns to heavy, wet slush that grabs your skis. Depending on aspect, elevation, and weather, the corn window on a given slope might only last an hour or two.

What Corn.Ski does

On corn.ski, you drop a pin and I'll tell you exactly when that slope corns out. In order to do this, I created a physics-based energy balance model to predict when and where corn snow will form. The end result is essentially a probability spread showing you the likelihood of corn snow forming at different times of the day. The model right now is a bit of a hack, but it's a useful start. The best way to help will be to let me know what you're seeing!

I present it kind of casually as a timeline of the day. Frozen, hard pack ice is first presented as ice - 🧊, then the corn window is presented as corn - 🌽, and finally the mush window is presented as a potato - 🥔.

Resources

If you're maybe as fascinated by this stuff as I am, here's some resources that I found helpful

Energy Balance & Radiation

• Male, D.H. & Granger, R.J. (1981). Snow surface energy exchange. Water Resources Research, 17(3), 609–627.
• Marks, D. & Dozier, J. (1992). Climate and energy exchange at the snow surface in the alpine region of the Sierra Nevada. Water Resources Research, 28(11), 3043–3054.
• Brutsaert, W. (1975). On a derivable formula for long-wave radiation from clear skies. Water Resources Research, 11(5), 742–744.
• Sicart, J.E. et al. (2006). Incoming longwave radiation to melting snow. Hydrological Processes, 20(17), 3697–3708.

Snow Metamorphism & Albedo

• Colbeck, S.C. (1982). An overview of seasonal snow metamorphism. Reviews of Geophysics, 20(1), 45–61.
• Raymond, C.F. & Tusima, K. (1979). Grain coarsening of water-saturated snow. Journal of Glaciology, 22(86), 83–105.
• Warren, S.G. (1982). Optical properties of snow. Reviews of Geophysics, 20(1), 67–89.
• Brun, E. et al. (1992). A numerical model to simulate snow-cover stratigraphy for operational avalanche forecasting. Journal of Glaciology, 38(128), 13–22.
• Avalanche.org — Corn Snow (Melt-Freeze Processes)

Terrain & Solar Radiation

• Horn, B.K.P. (1981). Hill shading and the reflectance map. Proceedings of the IEEE, 69(1), 14–47.
• Dozier, J. & Frew, J. (1990). Rapid calculation of terrain parameters for radiation modeling from digital elevation data. IEEE Trans. Geoscience and Remote Sensing, 28(5), 963–969.
• Dubayah, R. & Rich, P.M. (1995). Topographic solar radiation models for GIS. Int. J. Geographical Information Systems, 9(4), 405–419.

Snow Models & Downscaling

• Bartelt, P. & Lehning, M. (2002). A physical SNOWPACK model for the Swiss avalanche warning. Cold Regions Science and Technology, 35(3), 123–145.
• Liston, G.E. & Elder, K. (2006). A meteorological distribution system for high-resolution terrestrial modeling (MicroMet). J. Hydrometeorology, 7(2), 217–234.

Data Sources

• Open-Meteo — Weather & Elevation API
• NRCS SNOTEL — Snowpack Telemetry Network
• NOAA SNODAS — Snow Data Assimilation System
• USGS 3DEP — 10m Digital Elevation Model
• NOAA HRRR — High-Resolution Rapid Refresh
• NASA MODIS — Snow Cover & Albedo

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