After a dry period, deep mosoon moisture returned to northern Arizona with shower and thunderstorm ramping up.
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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.
After a dry period, deep mosoon moisture returned to northern Arizona with shower and thunderstorm ramping up.
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 21, 9:52 AM MST, 2 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 952 AM MST Wed Aug 21 2024 .SYNOPSIS...Monsoon activity will increase later today and into Thursday as moisture surges northward. After another round of storms on Friday, the weekend should see a return of dry conditions across most of northern Arizona. && .UPDATE...This morning's satellite and upper-air analysis shows a subtropical high pressure system broadly centered over New Mexico and west Texas. Flow around the high is pumping moisture northward into Arizona from the Gulf of California. Bands of cloud cover associated with this moisture can be seen over much of the state, although a notable region of mostly clear skies is visible over portions of east-central Arizona. At the surface, dew points have broadly increased by several degrees compared to yesterday morning. The largest increase in dew points has occurred over western Arizona due to low-level moisture advecting northward through the Colorado River Valley. For example, the dew point at Kingman, AZ, is currently 63°F, about 10 degrees higher than yesterday at this time. The upper-air sounding taken from near Flagstaff, AZ, measured 0.82 inches of precipitable water, which is only a modest increase from the 0.75 inches observed yesterday. However, cooling was observed in the 500-300 mb layer, indicating steeper lapse rates and more instability. HREF mean CAPE values show between 1000-1500 J/kg along and south of the Mogollon Rim, with lesser amounts north of the Rim. 0-6 km bulk shear ranges from 15-25 knots. This is on the lower side, but a few rotating storms cannot be ruled out. Today's storm motion is to the north-northeast at 15-25 mph. With the influx of moisture, flash flooding will be the primary hazard today. Storms will be moving quickly, so training storms will be necessary to produce flash flooding, except in areas highly sensitive to rainfall, such as slot canyons and burn scars. In terms of the overall forecast, storm activity is expected to pick up after noon over higher terrain before pushing northward into the valleys. Cloud cover may keep things somewhat subdued throughout the day over portions of Yavapai and western Coconino Counties, but clusters of storms that originated over southern Arizona this afternoon will likely lead to a second round of showers and thunderstorms as they sweep across northern Arizona overnight. The only forecast updates made this morning were to reduce the chances for storms this afternoon across Yavapai County to account for the impact of cloud cover there. && .PREV DISCUSSION /441 AM MST/...For Thursday, with plenty of moisture still in place, another round of scattered to widespread showers and thunderstorms look to develop. Areas that saw overnight rainfall may be a little subdued, but much like today, coverage will fill in through the afternoon. All and all, flash flooding looks to be the primary threat over the next couple of days. Storm motions of around 20 kts may limit the residency time of any single storm, but areas that see training storms or any especially sensitive areas could still see flash flooding. HREF PMM guidance mainly hits at areas from northwest AZ through south-central AZ for the greatest risk of heavy rainfall today, and then most areas along and north of the Mogollon Rim on Thursday. A few isolated strong to severe storms will also be possible, especially with the added dynamics from the nearby trough. The greatest chances for severe storms look to be over far northern Arizona today, and from about I-40 north on Thursday where better shear looks to be present. Friday through Sunday...Showers and thunderstorms remain on Friday, but the greatest coverage looks to be over eastern Arizona as drier air moves in from the west with the approaching trough. Chances for showers will continue to shift eastward through the weekend, with mainly dry conditions expected by Sunday. Breezier winds and cooler temperatures also look to ensue across much of the region for the weekend. Monday onward...Moisture looks to slowly increase by the start of next week as a westward propagating wave moves across northern Mexico. Chances for showers and thunderstorms look to return once again with the increasing moisture. Temperatures should also start to increase as high pressure tries to build back into the southwest. && .AVIATION...Wednesday 21/18Z through Thursday 22/18Z...SHRA/TSRA coverage will increase this afternoon, likely lasting through the evening and overnight hours. MVFR/IFR ceilings and visibilities, along with gusty outflow winds, are possible near +RA/TS. Winds outside of storms will be W to SW 5-15 kts. OUTLOOK...Thursday 22/18Z through Saturday 24/18Z...An active monsoon pattern continues with periods of SHRA/TSRA. Storm coverage decreases slightly on Friday. MVFR/IFR conditions and gusty winds possible near +RA/TS. VFR conditions are otherwise expected along with SW winds around 10 kts. Wind gusts increase Friday afternoon to around 25 kts. && .FIRE WEATHER...Today and Thursday...Widespread showers and thunderstorms will develop late this morning through Thursday. Heavy rain and gusty, erratic winds will be the main threats. Otherwise, winds primarily southwest 5 to 15 mph. Temperatures turning cooler. Friday through Sunday...Decreasing shower and thunderstorm coverage on Friday then turning mainly dry for Saturday and Sunday. Southwest winds 15 to 25 mph on Friday and Saturday decreasing to 5 to 15 mph on Sunday. Little change in temperatures. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && PUBLIC...RR/Humphreys AVIATION...RR FIRE WEATHER...MAS For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement
National Weather Service Flagstaff AZ
1139 AM MST Wed Aug 21 2024
AZZ006-007-211915-
Coconino Plateau-Grand Canyon Country-
1139 AM MST Wed Aug 21 2024
...A STRONG THUNDERSTORM WILL IMPACT COCONINO COUNTY THROUGH 1215 PM
MST...
At 1138 AM MST, Doppler radar was tracking a strong thunderstorm over
Grand Canyon National Park Airport, or 20 miles west of Desert View
Watchtower, moving northeast at 25 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...
Devil's Corkscrew, Pipe Creek Resthouse, Tusayan, BuggeIn Picnic
Area, Monument Creek Vista, South Rim, Buddha Cloister, Grand Canyon
National Park Airport, Hopi Point, Grandview Point, Yaki Point,
Plateau Point, Shoshone Point, Grand Canyon Village, Maricopa Point,
Phantom Ranch, South Rim Visitors Center, Moran Point, Pipe Creek
Vista, and Skeleton Point.
This includes State Route 64 between mile markers 231 and 237.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 3588 11219 3596 11228 3616 11209 3599 11190
TIME...MOT...LOC 1838Z 230DEG 24KT 3596 11218
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
McCollumThe Flagstaff radar (KFSX), 123 km away, was scanning. The volume nearest the first event began at 19:13 UTC.
1 hail, 1 flash flood. Local standard time, as filed.
One inch diameter hail was reported 5 miles west of Chino Valley.
The river guage on Carrizo Crreek showed a rapid 2 foot rise starting at 6 PM on August 22 and peaked at 1100 PM. The flow decreased and leveled out around 400 AM on Agust 23.
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, August 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: 1213233, 1213231.