A deep dive into Japan’s snow
The snowfall in Japan is remarkable not only in quantity but also in reliability; you can certainly get much bigger and deeper snow dumps in coastal systems such as Whistler or New Zealand…. but, what Japan offers is a level of reliability of powder snow that’s unmatched anywhere else in the world. If you’re booking a dream ski holiday, that reliability counts for a lot!
In this post, I’m going to share a bit about the underlying mechanisms that make Japan’s snow system so good. I’ll share some pointers on when and where to make your trip to maximize the chances of daily dumps of deep, dry powder. Finally, I’ll share some resources to use to track the weather while you’re in Japan. We’ll also share some deeper dive reading material such as academic papers if you want to learn more.
With a lake effect operating at a massive oceanic scale, Japan produces some of the world’s best snow. Cold, dry Siberian air picks up great amounts of moisture before being dumped on coastal mountains as high quality powder snow. The lowland satoyuki effect in Hokkaido holds the snowclouds in place longer, emphasizing this ‘lake effect’. FYI, Japan offers some excellent weather forecasting tools, from basic to very advanced, including the Japan Met Agency’s ‘nowcasts’.
LAKE EFFECT AT OCEANIC SCALE
The key to the massive snow fall in Japan is that it is heavily driven by ‘lake effect’ snow. But, this isn’t like the lake effect snow of North America’s Great Lakes region, or the famous Salt Lake City powder snows of the Wasatch range. Japan’s lake effect snow is really ‘sea effect’ snow… and that means bigger, deeper dumps.
Lake effect snow occurs when cold, dry air passes over a relatively warm water body. Water evaoporates, saturating the air and also warming it. As the air rises, often helped by flowing up and over hills or mountains, it cools and precipitates the moisture as snow.
The recipe is simple:
- Cold, dry air
- Relatively warm body of water
- Wind over hils causing lifting and cooling
Let’s look at these ingredients each in turn.
1. Cold, Dry Air
The source of the cold dry air is the Siberian High. This is a large high pressure system over Siberia. In the atmosphere, a high pressure system is generally caused by masses of cold air descendning from higher altitudes. In our case we see this cold air descending and flowing out from Siberia and across the Sea of Japan. The intensity, coverage and variability of the Siberian High is in turn heavily influenced by snow cover across the region (see The role of the Siberian high in northern hemisphere climate variability, Cohen, Saito and Entekhabi, Geophysical Research Letters Volume 28 Issue 2) .
2. Relatively Warm Body of Water
The Sea of Japan is our ‘lake’; the source of moisture that will go on to become that deep dry powder snow. Becasue it is fed by currents from the South, The Sea of Japan (the sea running along Japan’s NW coast) is relatively warm. The average temperature in Niigata on the east coast of Honshu never drops much below 10 degrees (celsius!). This large temperature differential with the cool, dry air coming off Siberia allows the air to pickup significant moisture. The term fetch is used to describe the length of the water over which the wind blows unobstructed. The fetch across the Sea of Japan is anywhere from about 400km between Russia and Hokkaido all the way up to about 900km between China and Honshu. Generally, the greater the fetch the more potential for the evaporation of moisture into the air. But also, the greater the fetch the more the air will warm up… We’ll discuss this when comparing Honshu and Hokkaido snowfall below.
3. Wind Over Hills Causing Lifting and Cooling
The fancy term here is orographic lifting. On making landfall the wind blows up and over some hills. As air rises, it expands. As it expands, it cools. As moist air cools, it’s able to hold less of that moisture, and so the moisture precipitates out of the air. If it’s cold enough, that precipitation falls as snow. In our case, those hills and mountains include areas such as the Japan Alps, the Niseko Range, and the Daisetsuzan Range in Central Hokkaido. Our air is fed full of moisture by the Sea of Japan. And, yes, it’s cold… and it SNOWS! And it SNOWS! And it SNOWS!
One last little gem that is particularly relevant to snowfall in Hokkaido is the presence of satoyuki or lowland snowfall patterns. This occurs when a temperature inversion exists in the atmosphere and the weather system is ‘held down’ by this layer. This allows for additional time spent ***dumping*** all that moisture onto the windward side of the mountains. It’s one of the reasons that the Niseko area does so well, where the altitude at the resort runs from a base elevation of only 260m (850ft) to just 1,200m (4,000ft) at the top.
A great way to understand how temperature is changing through the vertical atmosphere is to view a ‘sounding‘. This data is either coming from real-world measurements (aircraft, weather balloons) or from a numerical model. As we note below, Windy.com offers easy access to a forecast atmospheric sounding.
BEST TIMES TO VISIT JAPAN FOR SNOW
If you’re used to the weather in New Zealand, Australia, Europe, or the Western US and Canada, then our ‘snow storms’ in Japan are going to feel quite different. Those other regions of the world are dominated by large weather systems where massive storms blow through, dump a whole load of snow (quality variable… Sierra cement anyone?), and then there’s a few days of clear still weather. The snow systems in Japan, particularly in Hokkaido, tend to be gentler and more consistent. Rather than massive storms rolling through, the cold air outflow from Siberia kind of gets turned on like a tap and so it just dumps consistently and often day-after-day-after-day. It’s not unheard of to go a week or two at a time with 20-40cm (8-16inches) every day.
So then, when does the tap go on?
And when does the tap go off?
Japan generally has a shorter and more intense season of peak snowfall than other parts of the world. My friends in Utah are emailing me photos of their first day out touring in late October… and I’m still out riding my mountain bike. Expect to be getting solid snowfall from mid-December through to early March. Obviously you want a bit of a base built up so the best time to visit is probably about mid January through end of February.
Hokkaido vs Honshu
This section will probably get me some hate, but, it’s ultimately a game of probability. Honshu, and particularly the Japanese Alps, can receive massive amounts of snow each year. The higher elevation and higher moisture content in the air (that fetch remember) means that when it dumps… it really dumps. But, you are playing a bit more dice with the temperatures and so the snowfall, and resulting snowpack, can be a bit more variable. There’s obviously much bigger terrain in the Alps and it’s easy enough to tag on some time there before or after a trip to Hokkaido. You’ll find the northern parts of Honshu, the likes of Aomori, are closer to Hokkaido in their overall weather patterns.
WEATHER FORECAST MODELS
Most of the weather forecasts that we see from day to day are the result of numerical weather forecast models. These models involve simulating the behaviour of the atmosphere on super computers and then using the forcasts of those simulations to forcast the weather. Many of the world’s largest meteorological agencies make their forecast model data available for free or for a free nominal cost. This means that the data is very available on 3rd party websites. A few of my favorites.
Windy was originally focused on providing data for sailors and windsurfers but these days it provides a really nice user experience to view data from a number of weather models. The user experience is Spatio-temporal; this means that you can look at the outputs of the models on a map and scroll back and forth through time. Models supported include the NOAA (USA) GFS model, the German ICON model, and the European ECMWF model. This last model is one that is paid-for and so Windy is unique in providing access to it for free in this format. Another great feature from Windy is that it provides access to an atmospheric sounding view. TO access the sounding view, click on a location and select the airgram view.
Spot WX http://www.SpotWX.com
This site allows you to see the same sort of weather model data but in a different user experience. This time plotted as charts and graphs. It has a different set of weather models including high-resolution models in North America and global models elsewhere. It can be a bit hit or miss as to whether the non-US data is working at any point in time, but, it is a great service when it’s working.
You can also go to the source data for these sites. This includes the NOAA models, the ICON model and also more localized models from the Korean Met Agency NEMA model and Japanese Met Agency GSM, MSM and other models. The exact format the data takes will vary by agency; typically this is the underlying model (sometimes with some human intervention or interpretation) that’s being used to produce forecast synoptic charts.
Keep in mind that all of the ‘special’ snow forecast sites such as snow-forecast.com or opensnow.com will be using one or more of the off the shelf weather models as the basis of their forecasts. Taking the time to learn to work with the source data is a great investment. If you want to learn more about numerical weather prediction then The Weather Machine is a great book to read.
Weather Maps, Sattelite and Radar
If you like to read a more typical weather map then my favorite for the region are the forecast and analysis charts from the Korean Met agency. The Japan Met Agency also does a great set of forecast charts in aviation style.
The JMA provides excellent real-time data from its network of weather radars, probably amongst the best in the world. This is available in both a general precipitation mode as well as a snowfall-specific mode. These ‘NowCasts’ are also worth keeping an eye on when flying into or out of Sapporo or Asahikawa airport as they give a good indication of delay/cancellation risk too.
THE GREATEST SNOW ON EARTH?
And one last resource to really geek out on. Jim Steenburgh is a Professor at the University of Utah. He teaches both undergraduate and graduate-level atmospheric sciences including a course on “The Greatest Snow on Earth”. He’s a Japan fan and so there’s plenty of content and commentary on Japan in general and Hokkaido in particular. Key resources from Jim include:
- Academic papers at https://www.inscc.utah.edu/~steenburgh/home/ and in particular the 2020 paper Perspectives on Sea- and Lake-Effect Precipitation from Japan’s “Gosetsu Chitai”
A book titled “Secrets of the Greatest Snow on Earth”… Jim doesn’t quite get to admitting that Hokkaido has an even better snow system than Utah…. but he gets awfully close.
A blog site called Wasatch Weather Weenies which is very actively updated and includes lots of lay-person ready snow and atmospheric science content.
Maybe you’ve got other great resources that we’ve missed. Would love to hear from you in the comments and we can update this article with inputs.