The ninja knew that successfully forecasting rain and the wind could give them strategic advantages against the enemy. They studied the weather and this was called “tenmon.” Ninjas believed that
- If there are dew drops on spider nets, it would be a clear weather
- If there is a large ring around the moon, it is likely to rain
- If the mountains seem close, it is likely to rain
- If the stars are twinkling, the next day will be rainy
- If it is cloudy but not windy, it is not going to rain (fall season only)
- Ninjas also often set a fire to ablaze the enemy territory. It is very important to know when there will be a smooth dry wind called the “foehn effect” to accelerate the fire. The ninjas used kites in the morning to predict the dry wind in the afternoon.