Why is jerome so critical about weather forecasts?

In Chapter five they oversleep, only waking when Mrs. Poppets comes in at nine. Harris and J. are greatly irritated with George, and their mood grows worse when they learn that the day’s weather forecast is poor. J. digresses to complain about how often weather forecasts are inaccurate. He also concocts a hypothetical story about staying inside when the forecasts predict rain and missing a beautiful day, and then believing the forecast of sun the next day, but ending up wet. Ch. 5