A late-season surge of monsoonal moisture is sweeping across the U.S. Southwest, producing scattered thunderstorms, heavy downpours and a heightened flash-flood threat from Arizona to Southern California, according to multiple National Weather Service offices. Radar early Saturday showed showers stretching from Yuma County, Arizona, into Imperial County, California, while isolated cells in Colorado’s Front Range dropped as much as half an inch of rain in under an hour. The Weather Service issued a Flood Advisory for Calipatria in Imperial County as locally intense storms moved through the Coachella Valley and Los Angeles Basin. Further north, Sacramento forecasters kept a Heat Advisory in effect through 11 p.m. for California’s Central Valley, Delta, Coastal Range and adjacent foothills, warning of triple-digit temperatures. In Arizona, Extreme Heat Warnings remain for the lower desert regions, where overnight lows are expected to stay in the upper 80s to low 90s, offering little relief. Meteorologists cautioned residents and travelers to remain hydrated, monitor official alerts and avoid flooded roadways as the system continues to lift northward into early next week.