Monsoon moisture over northern Ariozna, very weak steering flow, and westerly winds provided ventilation aloft leading to slow-moving thunderstorms with locally heavy rain and 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 Ariozna, very weak steering flow, and westerly winds provided ventilation aloft leading to slow-moving thunderstorms with locally heavy rain and 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 Sep 7, 3:59 PM MST, 1 minute earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 359 PM MST Sat Sep 7 2024 .SYNOPSIS...Shower and thunderstorm activity will continue this weekend, especially over portions of Yavapai and Coconino counties. Temperatures will fall slightly, mainly due to cloud cover and shower activity. After a few lingering showers and thunderstorms Monday, expect dry, cooler and breezy weather for the remainder of next week. && .DISCUSSION...Slow-moving storms formed over the Mogollon Rim (and portions of NW Yavapai County) early this afternoon with reports of 0.5-1.0" of rain and dime-sized hail. Satellite imagery illustrates the upper level winds of 20-30kts ventilating the anvils to the east and allowing storm propagation to the west. We expect storms to continue to form across Coconino County and Yavapai County this afternoon with the diurnal heating. A few weaker storms are also possible over the higher terrain of Navajo and Apache Counties, though no heavy rainfall is expected there. There's some hints of precipitation continuing overnight, but currently keeping chances low at this time. Convective activity on Sunday will be farther to the north, with storms most numerous along and north of Interstate 40 and west of Hwy 89. Forecast instability does not appear to be as great as it was today, and with this the threat of strong thunderstorms will be somewhat diminished. However, the continued slow motion forecast will bring a threat of locally heavy rain accumulations. Increasing westerly flow will bring drier air into the area on Monday and decrease precipitation chances significantly. By midweek, a strong trough over the Great Basin will serve to sweep out any remaining moisture and bring windy conditions to northern Arizona - the first harbinger of Fall. Dry, breezy (even windy) conditions are expected through the rest of the week, with low temperatures dipping down into the 30s over the high country on Thursday and Friday. && .AVIATION...Sunday 08/00Z through Monday 09/00Z...Mainly VFR conditions persist through the period with SCT-BKN cloud cover near 10,000 feet AGL for the remainder of the afternoon. Expect isolated to scattered -SHRA/-TSRA through 02Z along and southwest of a KGCN-KFLG-KPAN line. Brief periods of MVFR visibilities, outflow winds above 30 knots, and mountain obscuration likely near the stronger storms. Widespread VFR conditions return after 03Z. Expect another round of isolated to scattered -SHRA/-TSRA to develop again after 19Z Sunday. OUTLOOK...Monday 09/00Z through Wednesday 11/00Z...Another round of isolated to scattered -SHRA/-TSRA is expected on Monday, mainly confined to western Coconino County. Drier conditions settle in on Tuesday. Outside of any gusty outflows from storms, plan on light south to west winds between 5-15 kts on Monday, becoming westerly on Tuesday. && .FIRE WEATHER...This Evening through Monday...Expect isolated to scattered showers and thunderstorms to continue through 8 pm MST this evening. Showers taper thereafter. Another round of storms is likely for Sunday afternoon across Yavapai and Coconino counties. Main threats include small hail, lightning, brief heavy rainfall, and gusty/erratic outflows of up to 40 mph. Storm coverage becomes less on Monday, confined to western Coconino County. Outside of outflow winds, anticipate light south to west winds, 10 to 15 mph, each afternoon. Tuesday through Thursday...Drier conditions are forecast from Tuesday onward with widespread afternoon humidity of 15 to 25%. Light westerly winds, 10 to 15 mph, are expected on Tuesday followed by stronger southwest winds, 20 to 35 mph, for Wednesday and Thursday. Temperatures remain warm through Wednesday, becoming cooler for Thursday. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && PUBLIC...BAK AVIATION...RR FIRE WEATHER...LaGuardia For Northern Arizona weather information visit weather.gov/flagstaff
Preliminary Local Storm Report
National Weather Service Flagstaff AZ
1225 PM MST Sat Sep 7 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1152 AM Hail 2 WSW Downtown Flagstaf 35.19N 111.68W
09/07/2024 M0.70 Inch Coconino AZ Trained Spotter
Spotter report.
&&
BakSpecial Weather Statement
National Weather Service Flagstaff AZ
118 PM MST Sat Sep 7 2024
AZZ016-018-072045-
Northern Gila County-Eastern Mogollon Rim-
118 PM MST Sat Sep 7 2024
...A STRONG THUNDERSTORM WILL IMPACT HIGHWAY 99 IN SOUTHERN COCONINO
COUNTY AND PORTIONS OF NORTHERN GILA COUNTY THROUGH 145 PM MST...
At 116 PM MST, Doppler radar was tracking a strong thunderstorm near
Bear Canyon Lake, or 11 miles northwest of Forest Lakes, moving west
at 5 mph.
HAZARD...Wind gusts up to 40 mph and nickel size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Horton Springs, Bear Canyon Lake, and Bear Canyon Lake Recreation
Area.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3451 11091 3439 11087 3433 11104 3450 11110
TIME...MOT...LOC 2016Z 077DEG 5KT 3444 11096
MAX HAIL SIZE...0.88 IN
MAX WIND GUST...40 MPH
JJSpecial Weather Statement
National Weather Service Flagstaff AZ
221 PM MST Sat Sep 7 2024
AZZ018-072145-
Northern Gila County-
221 PM MST Sat Sep 7 2024
...STRONG THUNDERSTORMS WILL IMPACT NORTHERN GILA COUNTY THROUGH 245
PM MST...
At 220 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from Pine to Kohls Ranch. Movement was southwest at
10 mph.
HAZARD...Wind gusts up to 40 mph and penny size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Horton Springs, Bear Flat, Mountain Meadows, Beaver Valley Estates,
Mesa Del Caballo, Water Wheel Falls, Ellison Creek Estates, Tonto
Village, Geronimo Estates, Freedom Acres, Strawberry, East Verde
Estates, Bonita Creek Estates, Whispering Pines, Star Valley, Flowing
Springs, Christopher Creek, Tonto Natural Bridge State Park, Tonto
Estate, and Ellison Creek Cascades.
This includes the following highways...
State Route 260 between mile markers 254 and 276.
State Route 87 between mile markers 254 and 272.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with these storms and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3429 11161 3441 11152 3443 11149 3441 11146
3442 11146 3442 11143 3438 11141 3440 11139
3441 11141 3442 11140 3439 11115 3437 11114
3438 11114 3437 11104 3435 11106 3434 11104
3437 11102 3433 11097 3421 11103
TIME...MOT...LOC 2120Z 022DEG 8KT 3437 11146 3431 11107
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH
JJSpecial Weather Statement
National Weather Service Flagstaff AZ
345 PM MST Sat Sep 7 2024
AZZ008-037-072315-
Yavapai County Valleys and Basins-Yavapai County Mountains-
345 PM MST Sat Sep 7 2024
...A STRONG THUNDERSTORM WILL IMPACT YAVAPAI COUNTY THROUGH 415 PM
MST...
At 343 PM MST, Doppler radar was tracking a strong thunderstorm over
Willow Creek Reservoir, or near Prescott, moving south at 10 mph.
HAZARD...Wind gusts up to 40 mph and half inch hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Thumbe Butte, Rancho Vista Estates, Willow Creek Reservoir, Iron
Springs, Embry-Riddle Aeronautical University, Acker Park, Goldwater
Lake Park, Wildwood Estates, Courthouse Plaza, Goldwater Lake, Lynx
Lake, Potato Patch, Watson Lake, .
This includes the following highways...
State Route 89 between mile markers 301 and 318.
State Route 89A near mile marker 318.
State Route 69 between mile markers 290 and 296.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3465 11256 3461 11235 3442 11240 3448 11269
TIME...MOT...LOC 2243Z 016DEG 10KT 3459 11246
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
JJThe Flagstaff radar (KFSX), 116 km away, was scanning. The volume nearest the first event began at 23:01 UTC.
1 flash flood. Local standard time, as filed.
The rive guage on Granite Creek in Prescott measured over a 6.5 foot rise in one hour betweeb 400 PM and 500 PM. The creek slowly dropped to near normal levels by 500 AM early the next morning.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2024Every state in 2024This day in weather historyWarnings in Arizona, September 2024
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: 1217246.