[2] Across the Desert Southwest, training showers and thunderstorms developed as they headed northward by an almost-undirectional flow, which was situated between a low-pressure area across California, and a retreating ridge of high pressure to the east of the low.

[3] Southerly flow between the low and the high pressure ridge caused moisture to be driven northward, surface-based convective available potential energy values of 1000–2000 j/kg yielded conditions for heavy rainfall-producing convective systems, and weak shortwaves combined with shear between 25–35 knots (29–40 mph; 46–65 km/h; 13–18 m/s) also provided thunderstorm development.

[14] The National Weather Service office in Las Vegas recorded 0.88 inches (22 mm) of rainfall, which was the wettest day in September in 11 years.

[27] Several businesses and homes, along with agricultural fields, were flooded in Niland, as more than 4 inches (100 mm) of rain fell east of the area.

[29] Yuma, Mohave, Pima, and La Paz counties were under a flash flood warning, and a funnel cloud was reported near San Luis.

[31] There were also wind gusts of up to 71 miles per hour (114 km/h) at Phoenix Sky Harbor International Airport, where several flights there were diverted,[32] and more than 27,000 power outages occurred in Maricopa County.

[34] Heavy rainfall caused mud and rockslides at Bryce Canyon National Park, and forced the closure of Navajo Loop Trail.