Japanese Winter Outlook 2018-19

Welcome to my Japanese long term seasonal forecast for 2018-19. As usual, I will examine all of the important models first for the season, and then examine all of the long term drivers, and it all, and come to a conclusion for the 2018-19 Winter. Time to get straight into it….


ECMWF is forecasting higher than normal MSLP over Japan during the winter. This means northwesterly winds will be less often and weakened for Honshu, and keep Lows away from Hokkaido.

UKMET also forecasts higher than normal MSLP over Japan, even higher than ECMWF over winter. This would cause westerlies over Hokkaido, and a struggle for lake/Sea effect snow for Central Honshu.

NMME(An American Multi-Model Ensemble) shows lower than normal precipitation anomalies for Central Honshu, which would indicate a weakened north westerly wind for Honshu.

The models are pretty unianimous in forecasting lower snowfall than normal for Honshu and Hokkaido to a somewhat lesser extent.


The El Niño-Southern Oscillation is currently heading towards a weak-moderate basin-wide event. Below is the ECMWF Seasonal forecast for January. Notice the warm anomalies stretching towards Indonesia from the Eastern Pacific, along the equator.

This means that we are going into a basin-wide event. A Eastern Pacific or normal El Niño generally means slightly lower chances for snowfall. But the correlations show that a Western Pacific or Modoki El Niño means a potentially very poor winter for Central Honshu, similar to a normal El Niño for Hokkaido however. The features of both an EP & WP Niño, tells me that ENSO is generally going towards a lower than average snowfall season for Japan.

However the Atmospheric ENSO component has started to become split from the Oceanic Niño component, that I just described. The EC & UKMET models are showing a more neutral ENSO/Nina-like Atmospheric outlook, so this may mean that ENSO’s impacts won’t hit as brutally as the basin-wide event would otherwise indicate, because the Niño can’t translate well into the Atmosphere. However there have been some signs of the atmosphere getting closer to Niño more recently, with a -SOI, and an ongoing +AAM event. This could be a temporary lapse, or an indication of things to come.


I’m going to repeat what I said last year on this topic, still a good summary:
“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.

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.”
The current Siberian Snow Cover is below average. The current forecast is for a big expansion over the next 15 days of snowfall over Siberia, into Western Russia.

We will probably end October fairly average in terms of snow cover IMO, so a neutral effect on the Siberian High, but maybe strengthening if we see a deeper snow depth, before the High starts to settle sometime in November.

Arctic Oscillation

As stated, a negative Arctic Oscillation or AO supports a stronger Siberian High, and also strengthens the East Asian Winter Monsoon, which increases snowfall for both Honshu and Hokkaido. So a -AO correlates with more snowfall.

Factors that allow a -AO include the Siberian Snow Cover, which based upon my forecast above, would correlate neutrally. Other factors include the Barents-Kara Sea Ice, that has been very low, helping to envoke a -AO, and the QBO, that during winter should average out to have slightly +QBO effects on the AO, which means a slightly less chance of a -AO. Other factors that support a -AO this winter is a lack of Laptev Sea Ice, potential for ridging to come from the Eastern Pacific Oscillation domain and potential for Scandinavian blocking throughout winter. In summary, I believe there is a fairly good chance of much of the winter, being spent in a -AO, with long term forecasts for November supporting this trend into winter.

EC supports a loose trend towards a -AO in winter.

Regional SSTs

Here is EC’s SST forecast for the Japan region in Jan.

The warm SSTs over the NW wind track from Siberia to Central Honshu, could warm/weaken those winds. They could also allow ridging to develop, if there is support around the region, or help deepen a low, should it come into the Sea of Japan. All of this isn’t good for Central Honshu. Hokkaido has roughly warmer than average SSTs to the north and the east, which could help deepen lows when they come into the region, supporting more snowfall in Hokkaido. ENSO, PDO and the -EPO support a stronger Aleutian Low that would help troughing in the Hokkaido region. In addition to the warm SST anomalies in the Sea of Japan, Hokkaido doesn’t look too bad.

ConclusionIt doesn’t look that great, but it isn’t a complete nightmare. The models paint a poor picture for Hokkaido, and an even worse picture for Central Honshu. It’s hard to be definitive with ENSO this year, but it will probably have a modest negative effect. The AO and SSTs help Hokkaido, with the former helping Central Honshu out, and the latter reducing it’s snowfall chances. My forecast is for Hokkaido to have a slightly above average snowfall season, and Central Honshu to have a slightly below average season IMO.

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.

This took a lot of work, so I appreciate your support. Starting in Late November, my long range outlooks for Japan will start! They will be produced every 2-3 weeks, looking out into the range of 10-30 days out. This season, I will explore climate Drivers as well, including the PNA, MJO and others. Stay tuned.

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. Regardless of the above, I wish everyone a great season of skiing.

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