Plentiful low level moisture across northern Arizona with dew points in the lower 50s lead to strong thunderstorms with heavy rain. This caused several flash floods across northern Arizona.
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.
Plentiful low level moisture across northern Arizona with dew points in the lower 50s lead to strong thunderstorms with heavy rain. This caused several flash floods across northern Arizona.
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, 3:27 PM MST, 1 hour 18 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 327 PM MST Sat Aug 12 2017 .SYNOPSIS...Expect typical monsoon weather conditions through the weekend. Drier air will bring a decreasing trend in storms beginning Monday, with isolated storms from Tuesday onward. && .DISCUSSION...Active afternoon across northern Arizona with scattered storms and isolated very heavy rain. Small hail was also reported. HRRR does show storms continuing through the night moving from west to east across Coconino County into central Navajo and Apache Counties. Low level moisture remains plentiful across northern Arizona through Sunday. The steering flow will push storms toward the E-NE. Fairly slow storm motion will bring a chance of localized heavy rainfall/flooding. Hail and gusty winds will also accompany the stronger cells. On Monday, a trough of low pressure will move out of the Pacific Northwest into the Great Basin. This will push monsoon moisture east of Arizona and will bring drier are over the state. Storm chances will drop to the slight chance category for most areas. By Tuesday, further drying is expected as the trough moves across Arizona. Breezy to windy southwest winds will also develop on Monday and Tuesday. Near average daytime temperatures should persist through at least Friday. && .AVIATION...For the 00Z package...Scattered showers and thunderstorms will continue through the afternoon and evening across northern AZ, with localized MVFR/IFR conditions in the strongest storms. Storm coverage and intensity will decrease after 03Z, with redevelopment expected during the daylight hours Sunday. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Daily rounds of showers and thunderstorms will continue through Monday, with temperatures slightly below normal. Tuesday through Thursday...A drier air mass will move back into the region with significantly decreased storm chances. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && PUBLIC...MAS AVIATION...KD FIRE WEATHER...KD For Northern Arizona weather information visit weather.gov/flagstaff
Hazardous Weather Outlook National Weather Service Flagstaff AZ 426 AM MST Sat Aug 12 2017 AZZ004>018-037>040-130230- Kaibab Plateau-Marble and Glen Canyons-Grand Canyon Country- Coconino Plateau-Yavapai County Mountains- Northeast Plateaus and Mesas Hwy 264 Northward-Chinle Valley- Chuska Mountains and Defiance Plateau- Little Colorado River Valley in Coconino County- Little Colorado River Valley in Navajo County- Little Colorado River Valley in Apache County- Western Mogollon Rim-Eastern Mogollon Rim-White Mountains- Northern Gila County-Yavapai County Valleys and Basins- Oak Creek and Sycamore Canyons-Black Mesa Area- Northeast Plateaus and Mesas South of Hwy 264- 426 AM MST Sat Aug 12 2017 This hazardous weather outlook is for Apache...Coconino... Northern Gila...Navajo...and Yavapai Counties in Northern Arizona. .DAY ONE...Today and Tonight Lingering monsoon moisture will lead to scattered showers and thundertorms, mainly during the afternoon and evening. Some local areas could see heavy rain lead to flash flooding, and this will be the main concern. Small hail and gusty winds are also possible with stronger cells. .DAYS TWO THROUGH SEVEN...Sunday through Friday Expect typical monsoon weather conditions Sunday with scattered showers and thunderstorms. Thunderstorm threats will include lightning, heavy rain, and small hail. Drier air will bring decreasing thunderstorm activity Monday, with little to no chance of storms Tuesday through Friday. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
Special Weather Statement National Weather Service Flagstaff AZ 303 PM MST SAT AUG 12 2017 AZZ015-122215- Western Mogollon Rim- 303 PM MST SAT AUG 12 2017 ...SPECIAL WEATHER STATEMENT FOR FLAGSTAFF... At 300 PM MST, trained weather spotters reported a thunderstorm producing pea-sized hail over Flagstaff near the I-40 and I-17 junction, moving east at 25 mph. Locations impacted include... Flagstaff and Walnut Canyon National Monument. PRECAUTIONARY/PREPAREDNESS ACTIONS... Motorists near the I-40 and I-17 junction should drive with extreme caution. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. && LAT...LON 3512 11171 3521 11174 3527 11158 3514 11151 TIME...MOT...LOC 2200Z 250DEG 21KT 3517 11166 TM
The Flagstaff radar (KFSX), 59 km away, was scanning. The volume nearest the first event began at 23:44 UTC.
3 flash flood, 3 heavy rain. Local standard time, as filed.
The river gauge on Beaver Creek at Montezuma Castle rose 3.36 feet in 90 minutes.
Thunderstorms produced heavy rain across portions of the Verde Valley. A four inch bird bath was filled to over flowing in 90 minutes just north of McGuireville. Water flooded their back yard and two inches of water was flowing over their road. A spotter reported 1.90 inches of rain in Cornville. Sand and gravel washed over their road as well.
A flash flood was reported at Shadow Rim Girl Scout Camp. Chase Creek was six to eight feet deep and over the banks. Water lines were damaged and roads were washed out. They received 2.45 inches of rain at the camp. Flash flooding was reported in the East Verde River at the Water Wheel (near Houston Mesa Road). That road was impassable from water and heavy debris in that location. The The East Verde River upstream was flowing five to six feet deep. A weather spotter claimed that it was the worst flooding in many years.
A thunderstorm produced 1.60 inches of rain in 45 minutes (heavy rain still falling a the time of the report). Water was starting to run in the normally dry washes.
The Arizona Department of Transportation reported that Highway 163 north of Kayenta was flooded between Mile Posts 399 and 400.
Thunderstorms produced heavy rain (2.25-2.49 inches) and pea sized hail (1/4-1/2 inch diameter) over a two hour period.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2017Every state in 2017This day in weather historyWarnings in Arizona, August 2017
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: 720659, 720661, 720641, 720658, 720651, 720663.