The Influence of Monsoonal Gulf Surges on Precipitation and Diurnal Precipitation Patterns in Central Arizona

Abstract

North American gulf-surge events, northward low-level influxes of cool and moist air from the Gulf of California, were statistically related to monsoonal precipitation and the associated diurnal cycle for the state of Arizona. Using Dixon?s Assessing Low-Level Atmospheric Moisture using Soundings (ALARMS) method as an indicator for gulf surges, a sequence of surge events was identified for the months of July and August for the period from 1957 to 2008. A network of Arizona precipitation gauges was stratified by the surge events occurring over this period. The findings indicate that gulf surges accounted for a significant majority of rainfall events in Arizona. This signal was most apparent in the drier central and southwestern deserts (including the Phoenix metropolitan area) and least apparent in the wetter eastern and southeastern portions of the state. Diurnal patterns in rainfall were identified for the Phoenix metropolitan area and its surroundings. A strong diurnal cycle was apparent in precipitation associated with both surge and nonsurge periods over the Phoenix area, with a greater tendency toward nocturnal precipitation during gulf-surge events. These findings suggest that dissipating afternoon thunderstorms east and northeast of the Phoenix area act as catalysts for the nocturnal storm development that is prevalent in this area.