Precipitation usually occurs when a high-pressure peak encounters a low-pressure peak. Meteorologists measure the speed of two peaks moving towards each other to determine when and where they meet to predict precipitation. From this we know:. ['Meteorologists are responsible for predicting precipitation.', 'Low pressure peaks always move towards high pressure peaks.', 'Precipitation does not necessarily require the appearance of low pressure peaks.', 'Some precipitation predictions are based on the general response of high and low pressure peaks.']