I just felt that it was troublesome to check the weather forecast beforehand.
The weather forecast said it would rain this afternoon.
The weather forecast was crazy off.
This is a combination of the words 天気, meaning "weather," and 予報 meaning "forecast." Put them together and you get the weather forecast!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.