Monsoon moisture over northern Arizona produced thunderstorms across the area.
Every event with a place to put it. Tap one for its entry below.
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 produced thunderstorms across the area.
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 11, 3:39 AM MST, 4 hours 51 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 339 AM MST Sat Aug 11 2018 .SYNOPSIS...Deep moisture will persist over central and southern Arizona, bringing afternoon and evening showers and thunderstorms to much of the area. Areas along and south of the Mogollon Rim will see the most activity through the weekend. Some storms will produce heavy rainfall, hail, and strong winds. && .DISCUSSION...Nocturnal convection continues to move across the area in the early morning hours with most of the activity now focused in the southern half of Yavapai county. This significant amount of activity this late into the overnight will likely impact initiation time of convection Saturday morning with cloud debris limiting heating early in the day before clouds dissipate. Limited available potential energy near the New Mexico border will decrease the potential for convection on the backside of an inverted trough. However some isolated showers will still be possible over the White Mountains and the eastern parts of the Mogollon Rim. Another round of afternoon and evening thunderstorms can be expected further west as storms initiate off the western parts of the Mogollon Rim Coconino and Kaibab Plateau before moving to the Southwest with steering flow once again around 20 knots out of the northeast. Some speed sheer is possible today through the storm growth zone, and could allow for slightly better organization and longer lived storms and will allow for a slightly increased threat of damaging hail from any of the stronger storms. Inverted v signature in the model soundings also point to a significant enough dewpoint depression that could allow for potentially damaging winds from thunderstorm downdrafts, especially over the lower terrain. Monsoonal moisture looks to remain in the area through the timeframe, however models are starting to come into better agreement over a downturn in activity on Monday and Tuesday where limited moisture in the mid levels will hammer storm development and propagation. By Midweek models show reinforcing surges of moisture moving back into the area, and diurnal convection becoming widespread for the rest of the forecast period. && .AVIATION...For the 12Z package...VFR conditions will continue across most of northern Arizona for the next 24 hrs. Expect isolated to scattered showers and thunderstorms to develop after 19z first over the high terrain and gradually move southwest. Winds light and northeasterly at 5-10 kts with afternoon gusts 10-20 kts. Local MVFR/IFR conditions possible near thunderstorms along with gusty and erratic winds. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered to widespread afternoon showers and thunderstorms will continue through the weekend as northeasterly flow and deep moisture remains locked in over northern Arizona. Strong outflow winds, hail, and frequent lightning will be possible with any thunderstorms. Monday through Wednesday...By Monday, moisture decreases north of the Mogollon Rim with minRHs 15-25% for most areas with better moisture remaining along the Kaibab Plateau. Expect mostly isolated thunderstorm coverage in these areas. Along and south of the Mogollon Rim, expect deeper moisture to remain with scattered to numerous thunderstorm coverage through Wednesday. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...Suk AVIATION...ET FIRE WEATHER...ET For Northern Arizona weather information visit weather.gov/flagstaff
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
745 AM MST SAT AUG 11 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0355 PM HAIL 5 S WILLIAMS 35.19N 112.18W
08/10/2018 M1.00 INCH COCONINO AZ TRAINED SPOTTER
STARTED AS PEA SIZED AT 3:50PM MST,
PROGRESSED TO QUARTER SIZE.
&&
TMThe Flagstaff radar (KFSX), 96 km away, was scanning. The volume nearest the first event began at 15:31 UTC.
3 hail, 1 flash flood. Local standard time, as filed.
Flash flooding closed Gene Taylor Ranch Road at Dobson Wash.
Hail up to golf ball sized (1 3/4 inch diameter) was reported at the KOA Campground 6 miles north of Williams. Another storm produced penny (3/4 inch).
Soft hail up to 1 inch in diameter shredded some plants. Metal structures were not damaged.
Hail the size of quarters to half dollars (1 to 1 1/5 inch diameter) fell in The Village of Oak Creek.
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: 781936, 781937, 781938, 781939.