GFS and EC Monthly Control show a snowfall event for Central Honshu and Hokkaido, starting on the 24th, after some rain for Honshu on the 22nd and 23rd. This roughly continues to fall in moderate-heavy amounts, until the early parts of the 26th.
Rain is forecast for Hokkaido and Honshu on EC Monthly on the 4th of March, after a dry week preceding. Moderate-heavy snowfall begins on the evening of the 4th, into the 5th.
Rain is forecast from the afternoon of the 4th, overnight, easing in the early hours of the 5th. Cold air is absent around Central Honshu at this extent of the model forecasts.
The Arctic Oscillation is in a very strong state in the short-medium term, and is likely to remain so into the long term. We want to see it in the negatives, which of course hasn’t happened very often this year.
Between the +IOD dominated climatic state in the tropics, and the strong tropospheric vortex dominating in the extratropics, we haven’t seen the feasibility for a strong snowfall season in Japan this year.
The Siberian High has mostly been weak, bar for a few brief periods, for the Japanese snowfall season. This has meant that the winds that deliver most of the snow to Honshu have not been driven into the region.
The brief strengthening about a week ago probably helps to explain the good snowfalls that have featured in early February. But now we have seen the Siberian High go weak again, and this is likely to continue for at least the next week per GFS. This means conditions are likely to deteriorate again.
Why has this been so? A weak Siberian High and a strongly positive Arctic Oscillation are roughly interlinked. This has also meant that the +EAMTs that have occurred this season have lacked the capacity to really assert control, because the Siberian base state, like the rest of the atmosphere, has not been accommodating to a snowfall-bearing process.
But speaking of positive East Asian Mountain torques, we may have found the last light left in this season. The 13th-17th Feb period is likely to feature a strong +EAMT (watch the ridge move from Siberia downwards into East Asia, this is the actual process of a +EAMT from a MSLP perspective). This is likely to improve the Siberian High, and create some decent snowfall conditions for the 3rd week of February, possibly continuing through to the 4th week of February.
Afterwards, as projected by the models, I’m expecting a decline in snowfall-bearing conditions in the last days of the month and into March, once the strong +AO retains control in the last 10 days of February, and weakens the Siberian High again.
So basically a poor week ahead, some improvement in terms of snowfall in the last two weeks of February, and then another decline in the last few days of the month, probably continuing through early-mid March.
This will be the last edition of the long range snow blog for Japan this season. I am grateful for everyone’s support this season. The actual long range outlooks over the season have been relatively decent for me in terms of verification.
But of course we have to deal with the seasonal outlook I issued in very late October last year. I called for an above average season with an early start for Honshu, and Hokkaido was forecast to be a slightly above average season.
This was pretty much a failure for me. Despite a few early moments in November, December flat-lined, and the early start wasn’t so. The snowfall season was below average. It just didn’t work out the way I thought it would. So a lot of learning to be done, but hopefully we will do better next year with some new knowledge and hindsight.
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. For those of you who don’t watch my other NH forecasts, or the Australian forecast in a few months, I shall see you probably in September or October for a (less extensive for me) seasonal outlook period.
Until then, enjoy the remainder of winter and the seasons to come.