Monsoon moisture over northern Arizona produced strong to severe thunderstorms.
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 strong to severe thunderstorms.
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 10, 3:28 PM MST, 22 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 328 PM MST Fri Aug 10 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...Afternoon convective thunderstorms have been slow to develop today, but are underway along the Mogollon Rim, White Mountains and northeastern plateaus and mesas. The deepest monsoonal moisture remains banked up south of the Rim across Gila and Yavapai Counties. Large scale high pressure remains stationed to our northwest over the Great Basin keeping a mean steering flow from the northeast to southwest. Winds aloft are slightly higher today than yesterday, resulting in a slight increase in wind shear favorable for some longer lived storms. Storms will continue to develop over the high terrain and gradually move southwest this evening. The high resolution models this afternoon show some agreement with a more organized convective system moving through central Arizona this evening and possibly into the overnight hours, and we have trended the forecast in this direction. The best potential for any severe storms or flash flooding will be over Gila/Yavapai Counties where the deepest moisture and instability are. Large hail and damaging wind are possible. Storm motion should limit the flash flood threat in general, but areas that receive multiple rounds of rainfall could experience flooding. The overall pattern remains relatively unchanged over the weekend with storms favoring the Rim southward through the afternoon with storms moving to the southwest. This will depend on nighttime convection and how much lingering morning cloud cover exists. Temperatures will remain near average for this time of year, except for some of the northern valleys such as near Winslow and Page that are quite warm due to the lack of shower activity. It looks like early next week will see a thinning of moisture resulting in less storm coverage, but moisture will increase again by the middle of the week as a deeper southerly flow develops. && .AVIATION...For the 00Z package...Scattered to numerous thunderstorms will continue this evening and possibly into the overnight hours across northern Arizona. Storms will move to the southwest through the evening hours. A few strong storms producing 40-50 kt winds and large hail are possible, mainly south of KFLG-KSOW. Isolated IFR in +TSRA, with otherwise primarily VFR conditions through the forecast period. Another round of scattered thunderstorms is forecast for Saturday afternoon. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Deep moisture will remain in place along and south of the Mogollon Rim and White Mountains. Expect scattered to numerous showers and thunderstorms in these areas through the weekend, with scattered storms mainly over the higher terrain north of the Mogollon Rim to the Utah boarder. Strong outflow winds, heavy rainfall, hail, and frequent lightning are the primary hazards. Monday through Wednesday...Expect scattered afternoon and evening thunderstorms through the period, with the best chances for storms continuing to be along the south of the Mogollon Rim and White Mountains. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...MCT AVIATION...MCT FIRE WEATHER...MCT For Northern Arizona weather information visit weather.gov/flagstaff
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1151 AM MST FRI AUG 10 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0430 PM HAIL PARKS 35.26N 111.95W
08/09/2018 E1.00 INCH COCONINO AZ TRAINED SPOTTER
NICKEL TO QUARTER SIZE HAIL FELL FROM A
SEVERE THUNDERSTORM THAT PASSED NEAR PARKS,
AZ. HEAVY WATER PONDING WAS ALSO REPORTED
FROM HEAVY RAINFALL ASSOCIATED WITH THIS
STORM.
&&
NLPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
159 PM MST FRI AUG 10 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 PM FLASH FLOOD 7 WSW ASH FORK 35.20N 112.60W
08/09/2018 YAVAPAI AZ TRAINED SPOTTER
HEAVY RAINS CAUSED 6-8" OF FLOWING WATER
ACROSS NORMALLY DRY RANCH LAND SEVEN MILES
SOUTHWEST OF ASH FORK. EIGHTMILE CREEK WAS
REPORTED TO BE OVERFLOWING THE CREEK BANKS
SOUTH OF I-40.
&&
NLThe Flagstaff radar (KFSX), 113 km away, was scanning. The volume nearest the first event began at 22:50 UTC.
3 hail. Local standard time, as filed.
Pea sized hail started at 350 PM MST and then progressed in size to quarter sized (1 inch diameter) y 355 PM MST.
A thunderstorm produced 1 3/4 inch hail 3 miles west of Seligman.
Hail damaged (dimple) the hood of a car as it traveled through the town of Young.
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: 781934, 781933, 781935.