Japanese Winter Outlook 2020-21

Hello all, welcome to my seasonal outlook for the Japanese snowfall season for the coming winter. Apologies for the later timing this year.

Climate Models

Per the blend of mainly European models (plus CFS) we see here for the NH winter, it is likely that we will see a much weaker than normal Aleutian low, and the possibility of Aleutian ridging. This is not a good sign for Hokkaido, that often relies on snow generated from Kamchatka lows.

The Siberian High looks like it will be weaker than normal at least on it’s northern side, with a positive AO outlook marked by high latitude troughs.

And finally unfortunately we see convection heading towards Japan from the Maritime Continent region, that has negative impacts on Japanese snowfall, increasing the likelihood of rainfall events.

Taking a look at two individual models, first CFS, we see similar patterns. We see the Aleutian ridging, and waning impact of the Aleutian low. We see more troughing than normal and a weaker Siberian High forecast north of Japan. You still see the NWly winds, but the deep cold impact of them would certainly be weakened by it.

With ECMWF model now, you see the same modelling. A strong level of support for Aleutian ridging, more troughing over Siberia (weaker Siberian High) and convection directly south of Japan. Not looking like good news from the models at all.

Sea Surface Temperatures

There are some necessary points to make here:

  1. The warm SSTAs surrounding Japan demonstrate the potential for more ridging around Japan for winter.
  2. The warm SSTAs in the Sea of Japan specifically allow a larger divide between warm sea surface temperatures and cold air aloft coming from Siberia. This could possibly increase lake/sea effect snowfall in terms of strength and duration of events.
  3. But on the other hand, more warmth in the atmosphere is not necessarily a good thing for snowfall either, and may lead to more rain, or less dry snowfall conditions (wetter snow).

Siberian High

“The Siberian High is an important, yet relatively unknown driver for snowfall in the Japanese Alps. A strong, stable Siberian High provides very cold air down towards Japan, except if the High is too far west. This cold air from the Siberian High creates the lake effect, that provides the massive snowfalls in the Japanese Alps.

Snowy Hibbo two years ago

The Siberian High is affected by a number of things, including snow cover in the region and the AO. A negative AO causes a stronger Siberian High. The Siberian High is also affected by the snow cover in Siberia during October and November. An above average Siberian snow cover creates an early, potentially more stable Siberian High. It also correlates with a negative AO.

Snowy Hibbo two years ago

The rise of the snow extent in Siberia was relatively average throughout October, if perhaps a little bit weak. However we saw a strong backoff in early November leading to below average snow extent for that time of year. In the past week or so, the snow extent in Eurasia has expanded rapidly and we have returned to average. We are likely to see a mildly negative impact on the development of the Siberian High, and a negative impact on Japanese snowfall.


In terms of ENSO impacts on Japanese snowfall, we are going to use this analog that I made in October (1985, 1989, 1996, 2000, 2001, 2008, 2011, 2018). We are looking at a basin wide/EP La Nina event, as one can see with this ENSO anomalies chart showing current conditions:

So we see certain patterns develop on this chart, that are not necessarily that bad:

  • A stronger than average Siberian High, particularly on the western side.
  • A decent Kamchatka low, playing off a North Pacific ridge pushed towards Alaska.
  • A strong tropical signal south of Japan.

So it is likely that this would mean a pretty decent season for Hokkaido and Northern Honshu, but we will possibly see more wet and warm lows come from the south and negatively impact ski fields in Central Honshu.


It is clear that the MJO will favour Phases 3-4-5 over the winter, which is not so good for Japanese snowfall with the possibility for more rain from the south. The best phase of the MJO for Japan is deeper into the Pacific at about Phase 7.

Arctic Oscillation

  1. Siberian Snow Cover during the months prior to winter is average to below average, so a +AO is mildly more probable, which does not Japanese snowfall.
  2. Arctic sea ice is lower than average, which helps to angle us towards a more -AO outlook, in particular low sea ice in the Barents-Kara Sea. This would be more beneficial to Japanese snowfall.
  3. The QBO is expected to have an effect of promoting a positive AO.
  4. The stratospheric polar vortex is stronger than normal at the moment, and is expected to stay like that into December and possibly beyond (linked with a +AO)

Because of the above factors, I expect a positive Arctic Oscillation to be dominant, not to say that a -AO is impossible at some stage though.


My basic contention for the Japanese snowfall season is that:

  • Hokkaido/Northern Honshu should expect an average season, perhaps mildly below average.
  • Central Honshu should expect a below average season with the probability of more rainfall events (but not necessarily a complete weakening in the snowfall mechanism)

Thanks so much for reading. 

Seasonal outlooks tend to have bias and errors, due to the fact that these forecasts are so far out. So don’t use these outlooks to make important decisions. These outlooks is meant to be interesting information, that can help to see what the season might be like. 

We should see the final winter outlooks for Europe and North America come out within the fortnight.

Thanks again for reading, follow me on Twitter @longrangesnow and subscribe to my email list by clicking on the tab on the main header above

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