As forecasted in my last long range outlook in December, the last few weeks have turned out great for Japanese snowfall. So let’s see what the climate modelling, and then the drivers have to say about the next month ahead.
Both GFS and EC Monthly Control are looking at a moderate-heavy snowfall event for Honshu from the 24th, and EC continues it through the 25th and 26th, with more moderate snow driving through to the 29th mostly isolated to Northern Honshu. Light-moderate snowfall begins in Western Hokkaido around the 25th per EC, through to the 29th.
31st Jan-1st Feb
Per EC Monthly, rainfall is brought by a low to Central Honshu on the 31st. Some snowfall in the backend may fall on the morning of the 1st.
EC Monthly projects a low to head up from the south to bring rainfall for the mountains in Honshu on the 6th-8th, and snowfall on the 8th and 9th to Hokkaido. There is a possibility for a colder backend for snow later on the 8th and 9th for Honshu.
The MJO is currently weakly passing into the Indian Ocean, and is expected to move over Australia and SE Asia. Phase 7 MJO (signal over the Pacific) is best for Japanese snowfall, so the MJO isn’t favourable for at least the next fortnight, but only mildly so with a weak signal.
The Arctic Oscillation has been negative since early December on the surface, and this has been brought into the stratosphere with a SSW. So all of that blue signifies a weakening of the polar vortex, which means more cold is sent down from the Arctic. This creates a setup that brings more snowfall for Japan. A negative AO is expected through January, and is favourable for Japanese snowfall.
The duration of the impacts of the stratospheric warming will have an impact on the duration of the favourable cold and snowfall impacts of the -AO.
However at least according to GFS, we are going to see that base state that has brought Japan so much snowfall over the past few weeks start to weaken:
The Siberian High has been very strong through much of December until this point, delivering very cold masses of air to Honshu and Hokkaido creating the lake effect snowfall that has been so prevalent lately.
Hokkaido also received snowfall from strong Kamchatka/Aleutian lows passing through the region, bringing benefits there. Together the strong Aleutian low and Siberian High helped bring the SSW into action and a +EAMT, which limits lows from the south, and locks into cold snow bearing setups from the north.
GFS is forecasting that these mechanisms are weakening. So this snowfall boom is likely to taper off in the last week of January, or possibly the first few days of February (rather similar to what EC Monthly is indicating). But it’s unlikely to be the very end, more like it is just getting turned down a fair bit.
GEFS is indicating a -EAMT state from the 20th of Jan, after a brief back to back -EAMT and +EAMT events in the next week. So from the week succeeding that, the pattern will start to shift to a less favourable one. So basically, enjoy the snowfall while it lasts…
Thanks so much for reading.
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.