It slipped my mind that the forecast had said that it would rain in the afternoon.
The weather girl said the forecast is calling for hot weather, starting tomorrow.
According to the weather forecast, this year Canada is expecting snow all year round.
A news report that covers things beforehand (before they happen) is a forecast. For example, a weather forecast is a 天気予報.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.