Meaning of 鰊曇 in Japanese

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Definition of 鰊曇

にしん(nishin) · かど(kado) · ニシン(nishin) 【鰊 ·鯡】

くもり(kumori) 【曇り ·曇】

(n) cloudiness; cloudy weather; shadow
昨日、東京は曇りでしたか。
Was it cloudy in Tokyo yesterday?

にしんぐもり(nishingumori) 【鰊曇り】

(n) cloudy weather near Hokkaido during the herrings season (from the third to the sixth lunar month)