Monsoon moisture over northern Arizona brought scattered thunderstorms with localized 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.
Monsoon moisture over northern Arizona brought scattered thunderstorms with localized 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 17, 10:04 AM MST, 3 hours 56 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 1004 AM MST Fri Aug 17 2018 .SYNOPSIS...A standard monsoon weather pattern will continue across much of Arizona today, with scattered, mainly afternoon and evening thunderstorms. A drying trend will develop over the weekend, with only isolated storms expected. Moisture increases again starting Tuesday, with a return to active monsoon conditions. && .UPDATE... Have tweaked pops and QPF to come better in line with satellite and surface observations. Expecting the rabidly eroding debris clouds to clear up shortly allowing for surface heating to once again create convective columns responsible for the bulk of the thunderstorm activity today. Storm flow is expected to be light from the southwest, leading to the main threat of the day being localized flooding. && .PREV DISCUSSION /300 AM MST/...Skies are mostly cloudy once again across northern Arizona. This could todays convection start, but scattered showers and thunderstorms are expected by early afternoon. A drying flow develops over the weekend due to the ridge position shifting west. Thus only isolated afternoon storms are expected. This drying appears to be short-lived as most longer range data indicates the ridge position moving into New Mexico late Monday. This should allow deeper monsoonal moisture to move back into northern Arizona, with increasing storm coverage starting Tuesday. && .AVIATION...For the 18Z package...Expect another active day with scattered to numerous showers and thunderstorms developing today. Brief MVFR/IFR conditions will be possible in the stronger storms, otherwise VFR conditions will prevail. Winds will be generally light, except near the stronger storms, where sfc wind gusts to 40 kts are possible. Storms will decrease after 02Z. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Expect another active day as deep moisture remains across much of the central and southern portions of the district. The airmass will begin to dry out on Saturday as west through northwest flow develops. Enough moisture will remain to keep a threat of convection over the southeastern portions of the district and dewpoints will remain relatively high. Sunday through Tuesday...Mainly dry conditions are expected Sunday and Monday, with light westerly flow and a drying boundary layer. There may be enough moisture for isolated convection over the White Mountains. Moisture returns to many areas Tuesday as a more favorable circulation develops. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...Suk/DL AVIATION...MAS FIRE WEATHER...DB For Northern Arizona weather information visit weather.gov/flagstaff
The Phoenix radar (KIWA), 139 km away, was scanning. The volume nearest the first event began at 21:01 UTC.
1 flash flood. Local standard time, as filed.
A stream gauge on Martinez Creek showed a two foot rise from dry to 1,400 CFS. Flooding was reported on Matthie Ranch Road.
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: 786247.