The Various Things of Seasons｜The Winter Weather Pattern in Japan　"Seikou Totei"
季節のあれこれ｜日本の冬の天気パターン「西高東低」

"Seikou Totei," often heard in weather forecasts around this time of year, turns out to be due to Japan's geographical factors.
天気予報でこの時期よく聞く「西高東低」。調べてみると日本の地理的要因だったんですね。

What is "Seikou Totei" （ West High, East Low）?

West High, East Low refers to a weather pattern over Japan characterized by high pressure in the west and low pressure in the east. Predominantly observed during winter, it's often referred to as a winter-type pressure configuration. This phenomenon leads to northwesterly winds blowing across the region.

西高東低とは何か

西高東低は、日本において西に高気圧、東に低気圧がある気象パターンを指します。主に冬に観測され、冬型の気圧配置とも呼ばれます。この現象により、北西風が地域を横切って吹きます。

How Siberia and China's Winter Cold Affects Japan's Weather

During winter, regions northwest of Japan like Siberia and China experience extreme cold, making the air heavier. This heavy air descends, compressing the air below it and creating high pressure. In contrast, over the Pacific Ocean to Japan's south, the air remains warmer and lighter, rising up and resulting in a thinning of the air and lower pressure.

シベリアと中国の冬の寒さが日本の天気に与える影響

冬になると、日本の北西にあるシベリアや中国のような地域はとても寒くなり、空気が重たくなります。この重い空気が下降して下の空気を押し潰し、高気圧を作り出します。一方、日本の南側にある太平洋上ではそこまで寒くないので、海側の空気は軽くて上昇し、空気は薄くなり低気圧となります。

Smoke Direction and Weather Predictions: An Old Japanese Proverb

The Japanese proverb "Smoke rising straight up indicates clear weather in the east, but rain if it drifts west" is based on the West High, East Low pattern. When smoke rises vertically during winter, it signifies the disruption of this pressure pattern and the cessation of northwesterly winds. This results in clear weather on the Japan Sea side but a deterioration in weather on the Pacific side, often leading to rain.

古い日本のことわざ：煙の方向と天気予測

「煙が東にたなびけば晴れ、西にたなびけば雨」という日本のことわざは、西高東低のパターンに基づいています。冬に煙が真っ直ぐ上がるのは、この気圧パターンの乱れと北西風の停止を意味します。これにより日本海側では晴れますが、太平洋側では天気が悪化し、しばしば雨になります。