Hourly data on the frequencies of all types of precipitation events, heavy precipitation events, trace precipitation events and thunderstorms for more than 100 stations in the United States were processed to generate statistics on the amplitude and phase of the diurnal and semidiurnal cycles at each station. Results are displayed on seasonal maps in a vectorial format that emphasizes the large scale geographical consistency of the diurnal variations. During summer each of the four parameters listed above displays a distinctive geographical pattern of diurnal variations. Thunderstorm frequency tends to be the most strongly modulated by the diurnal cycle; trace precipitation the least strongly modulated. Over the central United States the maximum frequency of severe convective storms occurs during the early evening; thunderstorms exhibit their maximum frequency around midnight, while most precipitation falls later in the night. These amplitude and phase differences offer some insight into the relat... Abstract Hourly data on the frequencies of all types of precipitation events, heavy precipitation events, trace precipitation events and thunderstorms for more than 100 stations in the United States were processed to generate statistics on the amplitude and phase of the diurnal and semidiurnal cycles at each station. Results are displayed on seasonal maps in a vectorial format that emphasizes the large scale geographical consistency of the diurnal variations. During summer each of the four parameters listed above displays a distinctive geographical pattern of diurnal variations. Thunderstorm frequency tends to be the most strongly modulated by the diurnal cycle; trace precipitation the least strongly modulated. Over the central United States the maximum frequency of severe convective storms occurs during the early evening; thunderstorms exhibit their maximum frequency around midnight, while most precipitation falls later in the night. These amplitude and phase differences offer some insight into the relat...