Monsoon moisture over northern Arizona brought thunderstorms with heavy rain and flash flooding. One thunderstorm produced a funnel cloud.
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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.
Monsoon moisture over northern Arizona brought thunderstorms with heavy rain and flash flooding. One thunderstorm produced a funnel cloud.
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 12, 2:40 PM MST, 35 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 240 PM MST Sun Aug 12 2018 .SYNOPSIS...Typical monsoon conditions will continue across Arizona this week, bringing scattered afternoon and early evening thunderstorms to much of the area. The highest chances will remain along and south of the Mogollon Rim. Some storms will produce heavy rainfall, hail, and strong winds. && .DISCUSSION...Scattered convection has fired along the Mogollon Rim and southwest of the Black Mesa and Chuska Mountains this afternoon. The environment south and west of the Mogollon Rim is conducive for severe thunderstorm development with SPC's mesoanalysis painting MUCAPEs around 2000 J/kg and effective bulk shear around 20 knots. Thunderstorms and the severe threat (1" hail, 60 mph winds) should continue through the late afternoon into the early evening hours. The latest HRRR progs convection ending across all of northern Arizona after 9pm MST. Mainly dry conditions are then forecast overnight. For Monday through Tuesday, high pressure will slowly meander southeastward into Arizona and become centered over the White Mountains Tuesday. This could result in a slight downward trend in afternoon convective activity. However, scattered storms along the higher terrain (Mogollon Rim, Black Mesa, and Chuskas) are still forecast each afternoon. Storm motions will be primarily instability driven with weak steering flow expected. For Wednesday through Saturday, the aforementioned high pressure then slides east into New Mexico and is progged to open up Gulf of California moisture into Arizona. A little more active monsoonal thunderstorm pattern is forecast during the latter half of the week. The medium range models around now a day slower with high pressure rolling into the Great Basin with Sunday now looking to show a drying trend. Will hold off on making any significant changes in the precip forecast given the model to model and run to run inconsistencies. Stay tuned. && .AVIATION...For the 00Z package...VFR conditions will continue across northern Arizona for the next 24 hrs with southwest and west winds at 5-10 kts and possible gusts of 10-20 kts. Showers and thunderstorms near KGCN, KFLG, KSEZ are beginning to move to the southwest near KPRC. Near thunderstorms, expect gusty and erratic winds along with possible localized local MVFR/IFR conditions. Storms will weaken after sunset. Thunderstorms near KFLG, KSOW and other high terrain areas Monday after 19Z. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered thunderstorms will develop both Monday and Tuesday afternoons along and south of the Mogollon Rim, Black Mesa, and Chuska Mountains. Storm motions will be erratic due to weak winds aloft. Wednesday through Friday...Afternoon monsoonal thunderstorm chances will continue each day primarily along and south of the Mogollon Rim, with a gradual uptick in activity forecast each day through Friday. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...TM AVIATION...NL FIRE WEATHER...TM For Northern Arizona weather information visit weather.gov/flagstaff
The Flagstaff radar (KFSX), 78 km away, was scanning. The volume nearest the first event began at 22:16 UTC.
1 funnel cloud, 1 flash flood. Local standard time, as filed.
Pictures of a funnel cloud were relayed to the National Weather Service. The time and location of the funnel cloud were estimated by using radar.
A swift water rescue was conducted along Prescott Street at the low water crossing of Agua Fria Wash. A motorist tried to cross the flooded roadway. The water was about 12 inches deep.
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: 786242, 781940.