Deep monsoon moisture over northern Arizona brought scattered thunderstorms with heavy rain and flash flooding.
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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 over northern Arizona brought scattered thunderstorms with heavy rain and flash flooding.
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 23, 10:11 AM MST, 3 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 1011 AM MST Thu Aug 23 2018 .SYNOPSIS...Deep monsoon moisture will remain over northern Arizona through Friday. This will result in good chances for afternoon and evening thunderstorms each day. A downturn in shower and thunderstorm activity is possible over the weekend and especially early next week. && .DISCUSSION...An active monsoon day is on tap for northern Arizona. Much of the area is enjoying partly to mostly sunny skies this morning. Scattered to numerous thunderstorms are expected to develop late this morning and continue into the afternoon hours with ample moisture in place. General storm motion will be from west to east. Some wind shear will be present today so stronger storms with hail and gusty winds are possible. The primary threat will be flash flooding especially in areas that have received significant rainfall over the past few days including western Coconino County and south into Yavapai County. Current forecast looks good and no updates are needed this morning. && .PREV DISCUSSION /418 AM MST/...Deep moisture remain over all of Arizona this morning. Satellite derived PW shows one to two inches along the Colorado River from Yuma to the Four Corners. Cloud cover extends along and south of a Prescott-Winslow-Four Corners line this morning. Showers and thunderstorms are still ongoing over southern Arizona this morning. A trough of low pressure moving through the Great Basin today will cause the winds aloft (above 18 kft/500 mb) to shift and become more southwesterly today over northwestern Arizona. This will help some storms become stronger today and move faster...roughly from a Prescott-Four Corners line today. Moisture values will change little today so scattered/numerous thunderstorms are expected today and Friday. A stronger southwest flow develops over the weekend for a downward trend in moisture and thunderstorm activity over northern Arizona. This downward trend could last well into next week. && .AVIATION...For the 18Z package...Sct-nmrs shra/tsra and isold +tsra by 18Z-19Z. Most active areas along and west of a KPGA-KGCN-FLG-KSOW line. Brief MVFR/IFR in the strongest cells. Light winds, except for thunderstorm outflows. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Monsoon moisture will remain over the district with good chances for showers and thunderstorms again today and Friday. Overnight activity is possible. Saturday through Monday...A drier air mass will slowly filter southward from the UT/AZ border starting Saturday. The drier air will lead to a downturn in shower and thunderstorm activity for areas north and east of the Mogollon Rim by Monday. The White Mountain region can still expect high chances for showers and thunderstorms. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...TPS/KD/MAS AVIATION...Peterson FIRE WEATHER...Peterson/KD For Northern Arizona weather information visit weather.gov/flagstaff
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1158 AM MST THU AUG 23 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0817 PM FLASH FLOOD 1 SW YARNELL 34.22N 112.75W
08/22/2018 YAVAPAI AZ DEPT OF HIGHWAYS
THIS IS A POST-EVENT REPORT. ARIZONA DEPT.
OF TRANSPORTATION REPORTS SR 89 IS CLOSED IN
BOTH DIRECTIONS FROM FLOODING AT MILE POST
277.4 (ABOUT 9 MILES NORTH OF SR 71).
&&
MCTThe Flagstaff radar (KFSX), 106 km away, was scanning. The volume nearest the first event began at 20:30 UTC.
3 flash flood. Local standard time, as filed.
Park Service personnel at Wupatki National Monument reported a flash flood and debris flow of volcanic cinders that caused damage to park housing. A vehicle was buried 1 to 2 feet deep in cinders.
At 554 PM, the stream gauge on Big Bug Creek in Mayer measured a 5 foot rise. At 630 PM, South Spring Lane was closed due to flooding near East Trails End Road. There was a 5 foot rise on Agua Fria River near Cordes Junction at 8:40 PM.
Rye Creek flooded Highway 87 at mile marker 241.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, August 2018
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: 786336, 786333, 786334.