Japan climate conditions in winter 2021/22
29 March 2022
Tokyo Climate Center (TCC), Japan Meteorological Agency (JMA)
https://ds.data.jma.go.jp/tcc/tcc
1. Climate conditions
Strong currents of cold air around Japan caused frequent heavy snowfall over northern towestern parts of the country’s Sea of Japan side and elsewhere from late December 2021
onward (Figure 1). Winter snowfall amounts were above normal in many locations on the Seaof Japan side, and values exceeded double the normal at some stations in western Japan(Figure 2). Average cumulative snowfall in heavy-snowfall areas 1 was actually significantly
below normal in the first half of December, but rose rapidly in the late December to matchthe climatological normal (Figure 3). The winter maximum snowfall depths were above normal
at many stations on the Sea of Japan side and elsewhere (Figure 4), with 12 of 331 stations
breaking the annual maximum records. Tsunan in Niigata Prefecture (Figure A1) recorded avalue of 419 cm on February 24 (Table 1). The ratio of stations observing top-three recordsnow depths was the fifth highest since 1985.
Variations in five-day running mean temperatures were relatively low from late December
onward, and below-normal temperatures persisted in eastern and western Japan (Figure 5).
Average winter temperatures were 0.5°C lower than normal in both eastern and western Japan(Figure 6).
Winter precipitation amounts were below normal in western Japan (Figure 7), especiallyin February, and seasonal sunshine durations were above normal.
2. Primary factors
The primary factors contributing to these climate conditions are illustrated in Figure 8.
⚫ The polar front jet stream (PFJ) and the subtropical jet stream (STJ) meandered southward
around Japan, and the winter low-level pressure pattern typically observed around thecountry was strengthened. These conditions facilitated four instances of strong cold-air⚫

⚫

1

inflow to the region (Figure 9).
Cold-air inflow triggered significant snowfall on the Sea of Japan side of the country. Inlate December a strong inflow event (Figure 1) and higher-than-normal sea surface
temperatures in the Sea of Japan may have increased the snowfall amount.
Southward meandering of the PFJ near Japan accompanied the formation of a blocking

As designated under the Act on Special Countermeasures for Heavy Snowfall Areas

https://www.mlit.go.jp/kokudoseisaku/chisei/crd_chisei_tk_000010.html (Japanese)

⚫

⚫

⚫

high over Eastern Siberia in the upper troposphere. Along with the blocking high, thetropospheric polar vortex over the Arctic region split, with partial movement southward
to just north of Japan.
The southward shift of the STJ to the east of Japan was likely influenced by its northward
meandering to the west of Japan, which was partly attributable to enhanced convective
activity in the area from the Philippines to eastern Indonesia in association with theprevailing La Niña event2.
Significant meandering of the jet stream in the area from the North Atlantic to Europe
and its downstream extension contributed to sustained meandering of the PFJ and theSTJ from Eurasia to Japan.
Frequent blocking-high formation over Eastern Siberia may have been influenced bysignificant northward meandering of the PFJ near the Gulf of Alaska. This meandering,associated with a Pacific-North American-like teleconnection pattern, was in turn likely
influenced by the distribution of convective activity associated with the La Niña event
active in the western tropical Pacific and inactive in the central and eastern tropical Pacific.

See also “Seasonal Highlights on the Climate System (December 2021 – February 2022)” onthe TCC website.
Note) This summary report is based on analysis and discussion in an ordinary session of theTCC Advisory Panel on Extreme Climatic Events on 11 March 2022. The Panel, consisting ofprominent experts on climate science from universities and research institutes, wasestablished in June 2007 by JMA to investigate extreme climate events based on up-todate information and findings. The current chair is Prof. Hisashi Nakamura from theUniversity of Tokyo. See TCC News No. 28 for more details on the outline and the frameworkof the Panel.

2The term “La Niña event” here refers to the conditions observed from autumn 2021 onward that did not

yet strictly meet the criteria of the phenomenon as of March 2022.

6-hour total precipitation
Weather maps

Infrared satellite imagery

amounts(Radar/RaingaugeAnalyzed Precipitation)

09 JST on 26th December

09 JST on 26th December

06-12

JST20212021

December 2021

on26thunit：mm

09 JST on 5th February09 JST on 5th February

06-12 JST on 5th February

2022

2022

2022

Figure 1. Left: Weather maps; middle: infrared satellite images; right:
precipitation distribution for 26 December 2021 and 5 February 2022 (forheavy snowfall on the Sea of Japan side of the country)

Figure 2. Ratio of snowfall amount for December 2021 – February 2022 to the climatologicalnormal of winter snowfall amount [%]The base period for the normal is 1991 – 2020. White dots indicate a ratio of 100%. Locations withamounts of 0 cm or normals less than 3 cm are not shown.

Figure 3. Average cumulative snowfall [cm] in regions designated under the Act on Special
Countermeasures for Heavy Snowfall Areas (1 November – 30 April)
Red line: cumulative snowfall for winter 2022 (as of 13 March)

Figure 4. Ratio of maximum snow depth for December 2021 – February 2022 to theclimatological normal of winter maximum snow depth [%]The base period for the normal is 1991 – 2020. The white-filled circles represent that the ratio is100%. Locations where this winter's amount was 0 cm or the normal value is less than 3 cm are notshown.

Table 1. Record-high annual maximum snow depth locations3 for December 2021 – February
2022
Prefecture
Hokkaido
Hokkaido
Hokkaido
Hokkaido
Hokkaido
Hokkaido
Hokkaido
Aomori
Gifu
Niigata
Shiga
Hyogo

3Location
Atsuta(厚田)
Eniwa Shimamatsu(恵庭島松)
Chitose(千歳)Ashibetsu(芦別)
Kuromatsunai(黒松内)Abira(安平)Ookishi(大岸)
Noheji(野辺地)
Sekigahara(関ヶ原)
Tsunan(津南)
Maibara(米原)
Uwano Kougen(兎和野高原)cm
198

Observationdate
8 February 2022cm
198

Previous record
date
19 February 2012154

23 February 2022

115

5 February 2006

1981

123

23 February 2022

77

28 February 2008

2006

130

14 January 2022

115

6 March 1999

1981

214

23 February 2022

204

13 March 1984

1981

127

23 February 2022

103

6 February 1996

1983

162

22 February 2022

116

3 March 2021

1983

115

17 February 2022

102

27 February 2012

2008

91

7 February 2022

79

9 January 1999

1997

419

24 February 2022

416

5 February 2006

1989

91

6 February 2022

83

27 December 2005

2001

208

24 February 2022

205

18 February 20122005

Start of observation
1981

Description
Joint record-highLocations among 331 weather/AMeDAS stations where snow depths have been recorded for at least 10years, either since the start of observation or since an environmental change such as relocation

Figure 5. Time-series representations of 5-day running mean temperature anomalies [°C]for December 2021 – February 2022
The base period for the normal is 1991 – 2020. Values in parentheses are winter mean temperature
anomalies for each region.

Figure 6. Distribution of mean temperature anomalies [°C] for December 2021 – February2022
The base period for the normal is 1991 – 2020.

Figure 7. Distribution of precipitation ratios [%] for December 2021 – February 2022
The base period for the normal is 1991 – 2020.

Figure 8. Characteristics of atmospheric circulation from December 2021 to February 2022

Figure 9. (a) Mean sea level pressure around Japan for winter 2021/22, and (b) winter East
Asian monsoon index(a) Contours indicate sea level pressure, and shading indicates the related anomaly (hPa).
(b) Winter East Asian monsoon index (Hanawa et al. 1988; sea level pressure difference between
Irkutsk and Nemuro, hPa) from 1 December 2021 to 28 February 2022 (five-day running mean). The
red line represents winter 2021/22, the dashed line represents the climatological normal, andshading represents the range of values each year from 1990/91 to 2019/20 (dark shading: 3 – 97%;
light shading: 10 – 90%). The larger values for the winter East Asian Monsoon Index indicate astronger winter pressure pattern around Japan. These data are based on the JRA-55 dataset.

3Figure A1. Climatologicalregions of Japan
JMA’s seven regional divisions
for climate monitoring andforecasting (the Sea of Japanand Pacific sides of northern,eastern and western Japan, andOkinawa/Amami)

References
Hanawa, K., T. Watanabe, N. Iwasaka, T. Suga and Y. Toba, 1988: Surface Thermal Conditionsin the Western North Pacific during the ENSO Events. J. Meteor. Soc. Japan, 66, 445-456.