Heavy rain raises flash-flood risk across Arizona burn scars, slot canyons and saturated ground

Day 1 Excessive Rainfall Outlook - September 16-17, 2026. Credit: NWS/WPC The Weather Prediction Center (WPC) expanded its Day 1 Moderate Risk of excessive rainfall westward across portions of southern and central Arizona in an outlook updated at UTC on September 16. The outlook is valid through MST ( UTC) on September 17. WPC said guidance showed individual cells producing rainfall rates of approximately 25–65 mm/h (1–2.5 inches/h) tracking farther west and north, increasing flash-flood potential and the area exposed to the threat. The National Weather Service (NWS) office in Phoenix said the Moderate Risk, Level 3 of 4, extends across the majority of Maricopa County and the Phoenix metropolitan area. Meteorologists described a Moderate Risk as representing at least a 40% chance of flash flooding within 40 km (25 miles) of a point. The Slight and Marginal Risk areas were extended farther west toward La Paz and Yuma counties and the Lower Colorado River Valley. Flood Watches remain in effect across large parts of Arizona. NWS Phoenix has watches covering Maricopa, Pinal and Gila counties through MST on September 16, with additional watch coverage across most of La Paz County and northern Yuma County. The office forecasts approximately 15–25 mm (0.5–1 inch) around Phoenix and areas to the west, approximately 50–75 mm (2–3 inches) across the eastern higher terrain, and localized totals above 75 mm (3 inches). Rounds of showers and thunderstorms are expected across central Arizona through Wednesday. The Phoenix Flood Watch states that many storms can produce rainfall rates exceeding 25–50 mm/h (1–2 inches/h), while training storms can produce higher accumulations where multiple cells cross the same location. Showers can linger into Wednesday night before activity decreases as drier conditions develop. Day 1 Excessive Rainfall Outlook – September 16-17, 2026. Credit: NWS/WPC Northern Arizona also remains under Flood Watch coverage. NWS Flagstaff forecasts persistent showers and thunderstorms during the active period, with heavy rainfall and flash flooding among the principal hazards. Its messaging identifies recent burn areas, slot canyons, and already saturated ground as locations requiring particular attention during heavy rainfall. NWS Flagstaff forecasts the greatest shower and thunderstorm coverage across its southern zones on Wednesday, with widespread activity continuing into Thursday morning and elevated flash-flood concern over recent burn scars. Storm coverage is forecast to decrease later in the week. Burn scars can respond rapidly to heavy rainfall because wildfire removes vegetation and can alter the ability of soils to absorb water, increasing runoff. NWS Flagstaff identified slot canyons and saturated ground among locations of concern during the current rainfall event.