# The Science of Powder (Part 1): Why Hokkaido snow behaves the way it does

Hokkaido snow will not hold a snowball. Part 1 traces it to the Sea of Japan, the winter monsoon and temperature — and why 30 cm is not always 30 cm.

- URL: https://www.ykhokkaido.com/en/blog/powder-science-01-why-hokkaido
- Published: 2026-09-05
- Section: Powder
- Series: The Science of Powder (part 1)
- Tags: Hokkaido climate, Snow crystals

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Most people try to make a snowball on their first Hokkaido morning, and most people are briefly confused. It will not hold. Open your hand and the snow falls apart into powder again.

That is not a figure of speech. It is a measurable physical property, and this series exists to turn "Hokkaido snow is dry" — a sentence everyone repeats — into numbers you can check and act on. Part 1 starts upstream: where this snow comes from.

## A humidifier the size of a sea

The Siberian high pushes cold air southeast all winter. Over the continent that air is cold and very dry. Then it has to cross the Sea of Japan.

In winter the sea is far warmer than the air above it, so heat and moisture pour into that cold layer from below. By the time it reaches Hokkaido's west coast it is cold and moist, and unstable near the surface. Terrain lifts it, the moisture condenses, and it snows.

The mechanism itself is not unique — lake-effect snow off the Great Lakes is the same physics. What makes Hokkaido distinctive is that the fetch across the sea is long **and the air stays cold after landfall, for weeks at a time**.

## "Dry" means air, not the absence of water

The shape a snow crystal grows into is set by the temperature of the cloud it grows in. Branched, dendritic crystals form best at cloud temperatures around −12 °C to −18 °C — a growth habit confirmed repeatedly in both laboratory and field work.

Branches catch on each other. When dendrites land and stack, they prop themselves apart and trap a great deal of air. **Dry snow is dry because there is more air in the pile, not because there is less water in it.**

Send those crystals through a layer near or above freezing on the way down and the branches melt back; the crystals stick together and stack with far fewer gaps. The same water then makes a shorter, denser pile.

## Turning it into one number

Comparing two snowfalls needs a shared ruler. That ruler is the **snow-liquid ratio**: how many centimetres of snow fell, divided by how many millimetres of water they melt down to.

The Japan Meteorological Agency's thresholds:

- 2.0 cm/mm and above → dry snow
- 1.0 cm/mm and below → wet snow

Put differently: one millimetre of water builds more than two centimetres of snow on a dry day, and about one centimetre on a wet one.

Which means "30 cm fell yesterday" leaves out half the story. Thirty centimetres of dry and thirty of wet differ by a factor of two in water content, and that changes how the surface supports you, how the board decelerates, and how many runs it takes before the slope is tracked out.

It is also why we never judge conditions on snowfall totals alone. Part 2 takes the snow-liquid ratio apart properly: how it is calculated, how temperature drives it, and why the snowfall figure in a weather forecast cannot be used to back it out.

## Three things to take away

1. Hokkaido powder needs two things at once: a long moist fetch across the Sea of Japan, and air that stays cold after landfall.
2. Physically, "dry" means a **high proportion of air** in the snowpack — not less water.
3. Compare snowfalls with the snow-liquid ratio, not centimetres. The dry-snow line is 2.0 cm/mm.

If you want the run and lift data for a specific resort, [Teine's runs & lifts page](/resorts/teine/guide) is a good place to start.

## FAQ

### Why is Hokkaido snow so dry?

Mostly temperature. The colder it is while snow falls, the more the crystals keep their branched shape and prop each other apart when they land. The same amount of water then piles up much higher. Inland Hokkaido holds below-freezing temperatures for long stretches.

### Is there an objective definition of "dry snow"?

Yes. The Japan Meteorological Agency splits snow by snow-liquid ratio — depth of snow divided by the water it melts down to. At or above 2.0 cm/mm is dry snow; at or below 1.0 cm/mm is wet snow. It is a measurable line, not a feeling.

### So is 30 cm of new snow a lot?

It depends which 30 cm. Dry snow can hold half the water of wet snow at the same depth, which changes how it supports you and how the board moves through it. Before asking how many centimetres fell, ask at what density.

## Sources

- Japan Meteorological Agency — dry/wet snow classification by snow-liquid ratio (dry ≥ 2.0 cm/mm, wet ≤ 1.0 cm/mm)
- Roebber et al. (2003), Improving snowfall forecasting by diagnosing snow density, Weather and Forecasting