Abstract
The diurnal variation of precipitation across California and Nevada has been studied by means of a harmonic analysis of 35 years of hourly precipitation data for 347 stations, and a regional probability of precipitation analysis for grouped stations. Results are shown for the cool (November-April) and warm (May-October) seasons.
For all measurable (>0.25 mm) precipitation events, the phase of the cool season diurnal cycle tends to peak between 0300–0900 LST along the coast, between 1000–1300 LST in the coastal mountains and the Sierra Nevada and in the Sacramento and San Joaquin valleys and between 0800–1200 LST in most of Nevada. Similar times are found during the warm season along the coast and in the coastal mountains while there is a shift to 1400–2000 LST inland across the Sacramento and San Joaquin valleys, the Sierra Nevada and Nevada.
For the heavier (>2.5 mm) precipitation events, the phase of the cool season diurnal cycle tends to peak from 1300–1800 LST at many locations. Exceptions include the eastern Sierra Nevada and Nevada, where a maximum near 1000 LST is found and along the coast and coastal mountains where a predawn maximum occurs. The transition from a late morning precipitation maximum along the coast and in the Saramento Valley to an early evening maximum in the San Joaquin Valley is well defined in the gap in the coastal mountains through the San Francisco Bay area.
During the warm season, precipitation tends to maximize between 1400–2200 LST at most interior locations and in portions of the coastal mountains in phase with the diurnal heating cycle. Coastal areas from Santa Barbara to San Diego retain a 0300–0700 LST precipitation maximum for the lighter precipitation amounts, characteristic of the well-known coastal summer stratus regime.
