Abstract: A weather forecasting apparatus, which is capable of accurately forecasting local atmospheric phenomena, has a vibration sensor attached to a tree for measuring an arboreal sound propagated through the tree. A voltage outputted from the vibration sensor depending on the measured arboreal sound is sent via an arboreal sound observing device to a data processing device. The data processing device includes a forecasting processor which determines the start or end of a rainfall based on the magnitude of the voltage, i.e., a sound pressure level corresponding to the magnitude of the sound pressure of the arboreal sound. When the sound pressure level rises, the forecasting processor determines the end of a rainfall, and when the sound pressure level drops, the forecasting processor determines the start of a rainfall. There is also disclosed a snowfall forecasting apparatus capable of accurately forecasting a local snowfall.