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Translation of the article
Updated on Aug. 9, 2012

How to Forecast Tomorrow’s Weather via Natural Laws: How to Read the Sky

By おひさま☆ (author of the original article)

Photo: nanapi.jp


Through the ages, people have said, “When swallows are flying low, it’s going to rain”. Have you heard of that?  You may think it is just an adage handed down by word of moth, but many of these sayings have a reason.
Today, I will write about how to predict tomorrow’s weather from the sky.

“The following day of the sunset glow is a fine day.”

Photo: nanapi.jp

The rays of sunlight travel through the atmosphere from the west, which means it is clear in the west with no clouds hiding the sun.  As the weather in Japan changes from the west, the fine weather in the west means that it will be fine in the east on the following day.

“A rainbow in the morning brings rain.  A rainbow in the evening brings a fine day.”

Photo: nanapi.jp

In the morning, the sunlight from the east makes a rainbow in the western sky.  A rainbow appearing in the sky tells us there is a high humidity there in the west.  As the weather is changing from the west,  it is going to rain.  A rainbow in the evening is made in the opposite sky, so the fine weather comes from the west.

“When contrails soon disappear, it is going to be fine weather.”

Photo: nanapi.jp

When the humidity is low in the high the sky where airplanes are flying, it is a clear sky where the contrails hardly form.  On the contrary, when the contrails stay for a long time, the humidity in the sky is high and there is likely to be some adverse weather.

“Morning dew in a spider’s web predicts fine weather.”

Photo: nanapi.jp

At night after a fine day, an air warmed during the daytime rises to the sky and cools down the air above it, making mist and forming dew on the ground.  When it is cloudy at night, mist is not generated.  Morning dew decorates a spider’s web in a fine day.

“When swallows fly low,  it is going to rain.”

Photo: nanapi.jp

When a low atmospheric pressure approaches, the temperature and the humidity level rise and many insects come out.  As their wings get heavy with the humidity, insects are flying around low.  Swallows fly low to get these insects.


Natural phenomena and natural life behavior are often related to the change in the weather.  It may be interesting to look into them.

Knowing the characteristic of clouds can help you predict the weather.  For more details, please refer to the following website.

Asobon NET: Forecast the weather with clouds (in Japanese)