Jun 22, 2012 · This, in turn, pulls the monsoon high south, exposing southern Arizona and New Mexico to the dry northern side of this high. As for September, El Niño conditions tend to increase the frequency of tropical Pacific Ocean storms, which can squeeze moist air from the Gulf of California into the Southwest. al., 2002). During the warm season, monsoon precipitation is strongly related to the positioning of the North American monsoon ridge. When the monsoon ridge is strong and displaced north of its mean climatological position in the Southwest, a wet and early monsoon occurs; dry, late monsoons correspond to a weak ridge, displaced to the south The Arizona/Great Basin onset of the 1999 North American monsoon was simulated using the MM5 regional scale model. This onset also produced a major flooding event in Las Vegas, Nevada. Resolution of the boundary layer was maximized, based on the Hong-Pan (or MRF) boundary layer scheme. Submesoscale Spatiotemporal Variability of North American Monsoon Rainfall over Complex Terrain MEKONNEN GEBREMICHAEL AND ENRIQUE R. VIVONI Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico CHRISTOPHER J. WATTS Departamento de Física, Universidad de Sonora Hermosillo, Sonora, Mexico Arizona Chapter of the American Meteorological Society, Annual Meeting. Arizona State University. Castro, C. L. (2018, January). The more extreme nature of North American monsoon precipitation in the Southwest United States.. 98th Annual American Meteorological Society Meeting. Castro, C. L. (2018, March).