Justin was watching a radio. Just after the midnight news there was a weather forecast: "It is raining now and will rain for the next two days. However, in 72 hours it will be bright and sunny." "Wrong again", snorted Justin. He was correct, but how did he know?
Considering day and night process:
In 72 hours it will be again midnight so it could not be sunny
Not considering that
He is "watching a radio" (I don't know if this was a hint to some other answer)
The forecast says it is raining now, but it isn't.