Deep monsoon moisture moving north across northern Arizona and southern Utah brought heavy rain from thunderstorms.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS FGZ wrote it up.
Deep monsoon moisture moving north across northern Arizona and southern Utah brought heavy rain from thunderstorms.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Flagstaff, AZ wrote its last area forecast discussion before the first event at Sep 2, 9:20 AM MST, 2 hours 40 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 920 AM MST Sat Sep 2 2023 .SYNOPSIS...Monsoonal moisture will provide one more day of showers and storms before we start trending dry Sunday into the start of next work week. Temperatures remain below normal before gradually moderating through the middle of next week. && .UPDATE...A few showers are being observed this morning across northern Arizona. We've updated the short term precip chances in the forecast to account for these. We remain in a moist, monsoonal air mass today with FGZ precipitable water values just under 1". This will be the last day for appreciable rain and thunderstorm chances. Similar to yesterday, we're also seeing substantial cloud cover that will delay or inhibit afternoon convection. We're starting to see some clearing across eastern Arizona, and expect to see some of this nudge westward allowing for some instability to develop. All in all, convection looks pretty scattered today with no definitive feature to organize things. The best coverage looks to be generally west of a Flagstaff to Page line where the deepest moisture remains. This, combined with recent rains, will lead to this area seeing the greatest flash flood threat today. The Flash FLood Watch for western Arizona continues through 11 PM MST tonight. Storms will dissipate this evening with most activity ending by 9 or 10 PM MST. && .PREV DISCUSSION /301 AM MST/...Today: continued favorable monsoonal flow will usher in high PWATS. The 00Z sounding yesterday measured a PWAT of 0.8 inches and guidance this morning indicates that PWATS could swell to above an inch in areas north of the Mogollon Rim. While cloud cover yesterday contributed to limited instability, HREF projections show clearing taking place late this morning into the early afternoon to get CAPE anywhere from 500-1500 j/kg available. So long as the clearing actually happens and the PWATs remain elevated, storms should be able to develop this afternoon west of the I17/HW89 corridor. In fact, local WRF projections show that we could have training thunderstorm problems for areas in the west. Meanwhile, the east looks to deal with more typical monsoon storm development and have enough storm motion to not lead to increased flooding concerns. Sitting in the middle of all that activity is the actual I17 and HW89 corridor (including Flagstaff, Sedona, Camp Verde, etc) that look to mainly make it through today mostly dry, minus any isolated showers and storms that might develop. Sky conditions in the east should definitely be clearer so confidence in storm development is higher there. Temperatures are going to remain below normal. Sunday: notably pulled POPs down for Sunday. PWATs will be steadily dropping as more zonal flow takes hold with the western trough shifting east. There will still be some isolated shower and storm activity, but nothing to run home about. Despite the decreasing moisture, the recent drop in temperatures combined with more zonal flow will help keep the cooler temperatures around. Next Week: zonal flow for the first part of the week, transitioning to unfavorable ridging for precip later in the week will mean dry weather for us. Temperatures will gradually moderate through the week, eventually returning to seasonal normal readings by roughly Wednesday and start to trend above normal. As of now, any rain chances remain beyond the extended forecast period, returning some time next weekend into the following week should ensemble guidance hold-up. && .AVIATION...For the 18Z TAF Package...Periodic MVFR cigs possible this morning. Then, expect scattered SHRA/TSRA to develop this afternoon with the greatest coverage south of a KGCN - KSOW line. Mostly VFR expected through the day, except for pockets of MVFR/IFR in TSRA. Storms diminish after 02Z with VFR area-wide expected thereafter. Surface winds SW 10-20 kts, with stronger gusts to 30 kts possible near TSRA. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Saturday and Sunday...Remaining seasonably cool with scattered to numerous showers and thunderstorms on Saturday becoming more isolated on Sunday. Away from showers and storms, expect mainly southwest winds at 10 to 20 mph. Monday through Wednesday...Dry, breezy and slighty warmer. Daily southwest winds 15 to 25 mph, with gusts to 30 mph. && .FGZ WATCHES/WARNINGS/ADVISORIES... Flood Watch through this evening for AZZ004-006>008-015-037-038. && PUBLIC...MCT/RKR AVIATION...MCT FIRE WEATHER...Peterson For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 69 km away, was scanning. The volume nearest the first event began at 18:58 UTC.
3 flash flood, 2 heavy rain. Local standard time, as filed.
Heavy rain fell across Coconino County. Some of the 24 hour rainfall amounts include (in inches): Arizona Snowbowl: 2.92, Bright Angel Point North Rim: 1.14, Four Springs RAWS: 1.13, Mable Canyon: 0.74, Tusayan: 0.73, and Jacob Lake 0.71.
Heavy rain fell across Yavapai County between September 2 and 3. Here are some 24 hour amounts (in inches) ending at noon on September 3: 11 miles SW of Prescott 1.28, 3 miles northwest of Camp Verde 1.25, 2 miles southwest of McGuireville 1.25, and 2 miles southwest of Cottonwood 0.93.
Heavy rain from thunderstorms over southern Utah and far northern Arizona caused flash flooding in the Paria River. The river gauge on the Paria at Lees Ferry (Colorado River) showed a two foot rise between 415 PM and 645 PM.
Heavy rain over Agassiz Peak and the area between Agassiz Peak and Fremont Peak caused a flash flood on the southern side of Agassiz Peak. The Kachina Trail had two deep channels cut through it about 400 yards apart. Those channels were 10 to 12 feet deep and extended above and below the trail. Some of the rocks in the flow were 3 to 5 feet in diameter. The two channels joined and the debris, water, and mud flowed southwestward. Most of the debris formed an alluvial fan just uphill from Freidlein Prairie Road. Water and mud did flow across that road.
Heavy rain over Agassiz Peak caused a flash flood on the northeastern side of the peak Peak into Locket Meadow. The water catchment in Snowslide Canyon was plugged with debris and damaged. One of the pump houses in the Inner Basin was damaged. The waterline that provides up to 30 percent of the water in Flagstaff during the summer was exposed and damaged in several locations. The access road around the water houses on Waterline Road was washed out.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2023Every state in 2023This day in weather historyWarnings in Arizona, September 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1131459, 1131464, 1131437, 1134956, 1144989.