A surge of monsoon moisture increased thunderstorms over northern Arizona with heavy rain, flash flooding, and hail.
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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.
A surge of monsoon moisture increased thunderstorms over northern Arizona with heavy rain, flash flooding, and hail.
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 Aug 29, 9:08 PM MST, 4 hours 52 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 908 PM MST Sat Aug 29 2020 .SYNOPSIS...Shower and thunderstorm chances will increase through Sunday. There will be a threat for heavy rain across Yavapai and Gila counties where a Flash Flood Watch is in effect through Sunday evening. Expect decreasing thunderstorm chances from Tuesday of next week onward with warmer weather returning by the end of the week. && .DISCUSSION... Just a few generally light showers are continuing across northern AZ this evening. However, more significant moisture across southern AZ will continue to push northward tonight and especially Sunday with showers forecast to increase. The focus for the precipitation is still expected to be along Gila and Yavapai counties. && .PREV DISCUSSION /239 PM MST/...Moisture continues to increase, especially across southern and into central parts of the state. The increased moisture and associated instability will be greatest for areas south of the rim across Yavapai and Gila counties where a Flash Flood Watch is in effect. The overall trend in forecast model data today suggests the greatest coverage of storms and heavy rain potential has shifted a bit later to Sunday. We have adjusted the forecast trends and precip chances to reflect this. Anyone with outdoor plans this weekend (especially south of the Mogollon Rim) should monitor the weather and have a good way to receive warnings. The chance for storms will continue into early next week but favor areas where the deeper moisture resides, generally along and south of the rim and White Mountains. A trough is forecast to move through the four corners region on Tuesday bringing an increase in wind speeds, followed by a drying trend. Drier weather is expected through the rest of the week as a strong ridge of high pressure building in from the west takes hold of the weather pattern. Not an unfamiliar pattern this year. In addition to the dry trend, we can expect temperatures to rise again by the end of the week becoming quite warm for early September. && .AVIATION...For the 06Z package...Widespread showers and storms are expected to develop Sunday and last through much of the day. Expect areas of MVFR/IFR and local +RA through the day, decreasing Sunday evening. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Expect scattered showers and thunderstorms through Monday across northern Arizona, with the best chance of wetting rain along and south of the Mogollon Rim on Sunday. Look for light winds except gusty near storms. Temperatures will be several degrees cooler. Tuesday through Thursday...Precipitation chances will decrease Tuesday as a drier northwest flow develops. Dry conditions are likely through the week with temperatures warming above average again by the week's end. && .FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through Sunday evening FOR AZZ008-018-037. && PUBLIC...KD/MCT AVIATION...KD FIRE WEATHER...MCT For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 71 km away, was scanning. The volume nearest the first event began at 08:59 UTC.
2 flash flood, 1 hail, 1 heavy rain. Local standard time, as filed.
Heavy rain fell over the Bush Fire scar and caused a 3-4 foot flash flood in Slate Creek. The water was black (ash) and muddy.
A trained spotter reported one inch diameter hail just north of Cordes Junction.
The Agua Fria river gauge at Old Black Canyon rose 1.8 feet.
Heavy rain caused boulders to fall across Interstate 17 four miles south of Bumble Bee.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2020Every state in 2020This day in weather historyWarnings in Arizona, August 2020
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: 918474, 918476, 918475, 918473.