Japan on the long term 22nd Dec

Welcome to the second Japanese long term snow update of the season, and the snow is starting to fall. The question is will it keep coming in heavy amounts. I use modelling and Teleconnections to discuss the weather moving into January.

6-10 Jan

EC Monthly shows a low dragging up the South Coast of Japan, bringing rainfall on the 6th to Central Honshu. As it moves northeast, it brings a more favourable flow from the northwest for Honshu and Hokkaido, bringing moderate-heavy snowfall on the 7th and the 8th, easing on the 9th, until another burst of heavy snowfall for Honshu comes on the 10th, and easing late at night.

11-12 Jan

Another lake/sea effect event occurs on the 11-12th of Dec, bringing moderate-heavy snowfall to Honshu and Western Hokkaido, according to EC Monthly.

14-15 Jan

On the 14th, a Low on EC Monthly brings heavy snowfall for Hokkaido for 6 hours or so, before moving south towards Honshu, with heavy snowfall developing later on the 14th and 15th there, before easing later on the latter day.

17-18 Jan

A low over Northern Hokkaido, brings very heavy snowfall to Hokkaido and Northern Honshu particularly, and heavy snowfall to Central Honshu as night falls on the 17th. The snowfall keeps going into the 18th, and eases through the day as the low moves away.

19-21 Jan

EC Monthly shows yet another lake/sea effect event, focusing moderate-heavy snowfall over the 19th through to the 21st, with consistent NW winds for Honshu.

Climate Drivers

We are currently in a roughly +AAM state. We are currently seeing a -EAMT (negative East Asia Mountain Torque) being brought into the overall global momentum budgets. This means that the jetstreams around the world are getting a bit slower than average. But on a more localised scale in East Asia, it brings lows to the East of the Himalayas over Eastern China, which allows more lows to potentially head towards Japan as warm rainfall events. It also makes creating north-northwesterly winds into Honshu, much harder, with lows on the East Asian Continent lurking. The good news is this is changing as I speak, and we will start to see a persistent +EAMT for the rest of the month and until the 5-10 Jan period, which brings highs to East Asia. This will bring good conditions for heavy snowfall in Japan over the rest of December, and the first 7-10 days of January. Then we should expect a relax in the pattern for 10 days or so. But then we should see a return to a +EAMT cycle in the final third of the month, and into Early February. Given the current +AAM background state, the relax in pattern shouldn’t be too bad for Japan.

Follow the red line for my EAMT forecast into the new year.

Another major event occurring in the next 10 days is a Sudden Stratospheric Warming. This below shows the weakening on EC just before the end of the year.

This will induce high latitude (polar) blocking, and will assist the restrengthening of the Siberian High and therefore the East Asia Winter Monsoon cycle. Along with the +AAM, this brings an Aleutian Low, able to send offshoots from the Kamchatka region, down to Hokkaido, as the Tropospheric Polar Vortex splits apart on pressure from the SSW in Early-Mid January. This means good news for Hokkaido particularly, but also for Honshu, with colder air in the region, more options for a +EAMT/Jet strengthening, and a stronger Siberian High.

Here is the EPS-46 forecast showing a negative Arctic Oscillation (a result of high latitude blocking from the SSW) throughout all of January. CFS shows a +AO until Jan 10, delaying the cold airmasses to later stages of January with a -AO later on in their forecast.

So overall the model outlook looks good. And the +EAMT pattern and a stronger jetstream off East Asia associated with it, should create a great Xmas-NY period for snow-lovers. And plenty of options for cold nodes to hit Japan in January with the SSW and -AO forecast. Looks like a good period for snowfall in both Hokkaido and Honshu IMO.

Thanks so much for reading. I hoped you enjoyed reading it.

Disclaimer: There is low skill asssociated with using long range model forecasts to find snow systems.

Thanks again for reading this Japanese long range snow forecast, 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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