Determining Gulf Surge Contributions to NAM Precipitation Using Observational and Reanalysis Data

The North American Monsoon (NAM) contributes nearly half of the annual accumulated precipitation in the desert southwest region of the United States. In the core NAM region, warm season northward surges of low-level, cool, moist air from the Gulf of California, or gulf surges, are thought to be a significant contributor to this total. Previous studies have found that these surges of moisture can enhance thunderstorm development over Arizona. This investigation is designed to examine the relationship between the trend of NAM precipitation and the gulf surge. Initially, an objective methodology is designed for identifying gulf surges in Global Historical Climate Network (GHCN) data recorded at the Marine Corps Air Station (MCAS) in Yuma, Arizona using criteria derived through joint collaboration with the National Weather Service. Criteria that must be met include an average daily dew point temperature of 18 degrees C or above combined with prevailing wind directions between 160 and 180 degrees. Surge day wind directions are used to verify the gulf surge related moisture transport for the list of surge onset dates. Accumulated monsoon precipitation is further analyzed using Climate Prediction Center (CPC) reanalysis data to identify rainfall amount contributed by gulf surges. Enhanced precipitation extremes have been observed in global monsoon regions. The gulf surge criteria developed will be used in regional climate model (RCM) climate change projections for NWP-type extreme event simulations.