During the East Asian Winter Monsoon, which over Japan features quasi-persistent northwesterly to northerly flow between the Siberian High and Aleutian Low, frequent cold-air outbreaks drive sea-effect storms near the Sea of Japan coasts of Honshu and Hokkaido Islands. Mean annual snowfall exceeds 500 inches in some mountain areas, much of it falling from December to February.
This year, however, the winter monsoon has been more of a winter "nonsoon." Snow depth observations as of today, 22 January, show many sites with under 50 cm of snow and only four over 100 cm (about 40 inches).
|Snow depth observations in cm. Source: http://www.data.jma.go.jp/obd/stats/data/mdrr/snc_rct/index_snc.html.|
This is unusual as nearly all sites are well below average, especially on Honshu where many sites are below 40% of average. One can find a few sites in northeast Honshu that are above 100%, but these are not in the heavy snow region near the Sea of Japan and thus snowpack in those areas is still scant. For instance, Sannohe in Aomori Prefecture is at 142% of average, but that's with only 27 cm on the ground.
|Percent of average snow depth. Snow depth observations in cm. Source: http://www.data.jma.go.jp/obd/stats/data/mdrr/snc_rct/index_snc.html.|
Near Niseko Resorts on Hokkaido, Kutchan currently has a 78 cm snow depth, which is only 61% of its 128 cm average on this date. Kutchan is near the base of Niseko and snow depths are probably greater on the mountain, but with records going back to 1944, it does illustrate the unusual low-tide conditions.
Perhaps not surprisingly, the deepest measured snowpack, indicated by the reddish-orange square in the top image above, is Sukayu Onsen in Aomori Prefecture on the north end of Honshu. Sukayu Onsen has a mean annual snowfall of 694 inches, so a bad year there is still better than a good year most anywhere else. There, in the Hakkōdo Mountains, the snow depth is 191 cm, but average is 248 cm.
One reason for the "nonsoon" so far this winter is that the Siberian High and Aleutian Low are weaker than average. Below is an analysis of the sea level pressure "anomaly" (or departure from average) for the one month period ending January 15. Negative anomalies over much of northern Eurasia are consistent with a weak Siberian High and positive anomalies over much of the north Pacific are consistent with a weak Aleutian Low.
One might ask why those pressure systems are weaker than average. Ha ha. I don't know the answer to this and I don't have the time to investigate. You get what you pay for with the Wasatch Weather Weenies blog. If you want me to investigate further, buy me a ticket to Hokkaido.