Proverb / Kotowaza
朝虹はその日の洪水
A weather proverb stating that seeing a rainbow in the morning is a sign that heavy rain will follow later that day.
A morning rainbow is a flood for that day.
Quick Answer
A weather proverb stating that seeing a rainbow in the morning is a sign that heavy rain will follow later that day.
- Literal Image
- A morning rainbow is a flood for that day.
- How to Use It
- Used to warn others of an upcoming change in weather or to explain why one expects rain despite a clear morning with a rainbow.
Meaning
This expression is a piece of weather lore suggesting that a rainbow appearing in the morning predicts heavy rain or flooding before the day ends. The saying is based on the observation that morning rainbows appear in the west, opposite the rising sun. Since weather patterns in Japan move from west to east, a rainbow in the western sky indicates that rain clouds and moist air are approaching.
Literal Image
A morning rainbow is a flood for that day.
How to Use It
Used to warn others of an upcoming change in weather or to explain why one expects rain despite a clear morning with a rainbow.
Tone
Informative and cautionary; used as practical advice based on nature.
Examples
朝虹はその日の洪水と言うだけあって、今朝きれいな虹が出ていると思ったら、午後には激しい雨になった。
Just as the saying 'a morning rainbow means a flood' suggests, it rained heavily this afternoon after a beautiful rainbow appeared this morning.
農家のおじいさんは「朝虹はその日の洪水だ、今日は外での作業を控えた方がいい」と孫に教えた。
The old farmer taught his grandson, 'A morning rainbow means a flood; you should avoid working outside today.'
朝虹はその日の洪水という昔からの天気の言い伝えには、科学的な根拠もあるらしい。
It seems there is a scientific basis for the old weather saying that a morning rainbow means a flood.
Learning Notes
Key Vocabulary
The kanji are relatively simple, but the sentence structure and meteorological context make it an idiomatic expression for intermediate learners.
朝
あさ / asa
morning
虹
にじ / niji
rainbow
その日
そのひ / sono hi
that day
洪水
こうずい / kozui
flood
Usage Profile
Misread Risk
This is specifically a weather-related prediction and should not be used as a metaphor for general bad luck.
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Origin
This is a piece of weather wisdom passed down in Japan from ancient times. When a rainbow is visible in the morning, it appears in the west, indicating that moist air is flowing in from that direction. As weather patterns in Japan move from west to east, a rainbow in the west serves as a sign of approaching rain clouds. This knowledge represents the accumulated experience of people working in agriculture and fishing who relied on sky-reading for their safety and work.
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Source Note
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