High pressure centered over The Four Corners area brought a moist southerly flow over northern Arizona. This allowed thunderstorms with heavy rain to form over parts of northern Arizona resulting in several flash floods.
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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.
High pressure centered over The Four Corners area brought a moist southerly flow over northern Arizona. This allowed thunderstorms with heavy rain to form over parts of northern Arizona resulting in several flash floods.
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 Jul 21, 9:16 AM MST, 3 hours 14 minutes earlier.
Area Forecast Discussion National Weather Service Flagstaff AZ 916 AM MST Wed Jul 21 2021 .SYNOPSIS...Another round of scattered showers and thunderstorms will develop today. Localized flash flooding is likely with the stronger storms. The threat of flash flooding only expands by tomorrow and into the weekend as thunderstorm activity becomes widespread across northern Arizona. && .UPDATE...Visible satellite imagery this morning shows slowly clearing debris clouds over northern Arizona. These conditions, with the continued moist profile captured on the 12z FGZ sounding, will promote another day of scattered to numerous thunderstorms over northern Arizona. High resolution models continue to prog initiation around 1000-1100 later this morning. As has been the case, continue to look for threats of flash flooding in localized areas of northern Arizona this afternoon and evening, along with some hail. Beyond small edits to the temperatures, no updates were made with the morning update. && .PREV DISCUSSION /332 AM MST/...A favorable monsoon pattern remains in place with anticyclonic high pressure centered over the four corners and ample moisture to fuel daytime showers and thunderstorms. A westward moving weather system will interact with this moisture later this week to bring even more widespread rain and thunderstorms with potential for heavy rainfall. For today, overnight convection continues to spread mid level cloud cover across central Arizona early this morning. Cloud cover should thin through the morning hours but may lead to a delayed start in thunderstorm initiation this afternoon due to delayed daytime heating. Nonetheless, a moist monsoon air mass remains in place and will fuel another round of showers and thunderstorms today. Weak steering flow will generally move storms to the west. Locally heavy rain will continue to be the primary threat, but a few stronger storms are also possible. Attention quickly turns to an upper level wave that is forecast to track westward across Texas and New Mexico Thursday and Friday and into Arizona Friday night through the weekend. This is a unique pattern during the monsoon and is not something we see every year. The westward tracking wave moving into a very moist monsoon air mass will provide dynamic lift and additional wind shear to support much more organized convection with widespread rain and thunderstorms. The added dynamic support will keep storm activity going well into the evening and nighttime hours later this week and weekend. Given the recent amounts of rainfall and flooding already observed in northern Arizona and the potential for multiple rounds of heavy rain later this week, we have issued a Flash Flood Watch for most of the area from Thursday afternoon through Saturday evening. Stay updated with the forecast this week, especially if you have any outdoor plans. In addition to the flood threat, the added wind shear may support some stronger storms as well with hail and strong wind not out of the question. The aforementioned wave remains over Arizona through Sunday keeping high chances for rain in the forecast. By Monday, the wave begins to lift northward allowing a more typical pattern to return with less coverage of showers and storms. && .AVIATION...For the 18Z package...Expect mainly VFR conditions for the 24 hour TAF forecast period. There will be scattered to numerous thunderstorms from 18Z-03Z, with MVFR conditions in the stronger storms. Scattered showers and isolated storms may persist from 03-07z east of KFLG, although with less coverage and intensity. Surface winds outside of storms will be generally light. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Scattered to numerous afternoon and evening showers and thunderstorms are expected today and Thursday. Some storms will produce locally heavy rainfall amounts, especially by Thursday. Expect light winds and near normal high temperatures outside of any storms. Friday through Sunday...Expect widespread showers and thunderstorms Friday and Saturday, with less coverage by Sunday. Wetting rains and locally heavy rainfall are probable, with activity persisting in the overnight periods. Significant Flash Flooding possible from Thursday afternoon through Saturday evening. && .FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch from Thursday morning through Saturday evening FOR AZZ006>008-011>018-037-038-040. && PUBLIC...NL/MCT AVIATION...NL FIRE WEATHER...Peterson For Northern Arizona weather information visit weather.gov/flagstaff
Special Weather Statement National Weather Service Flagstaff AZ 1019 AM MST Wed Jul 21 2021 AZZ008-037-211745- Yavapai County Valleys and Basins-Yavapai County Mountains- 1019 AM MST Wed Jul 21 2021 ...SIGNIFICANT WEATHER ADVISORY FOR YAVAPAI COUNTY JUST SOUTH OF PRESCOTT UNTIL 1045 AM MST... At 1017 AM MST, Doppler radar was tracking a strong thunderstorm over Groom Creek Subdivision, or near Prescott Valley. This storm was nearly stationary. Penny size hail and winds in excess of 40 mph will be possible with this storm. Locations impacted include... Prescott, Downtown Prescott, Ponderosa Park, Groom Creek Subdivision, Indian Hill West Prescott, Oak Knoll Village, Lower Wolf Creek Campground, Upper Wolf Creek Group Campground and White Spar Campground. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 3454 11240 3445 11238 3442 11253 3455 11254 TIME...MOT...LOC 1717Z 087DEG 1KT 3449 11244 JJ
Special Weather Statement
National Weather Service Flagstaff AZ
1203 PM MST Wed Jul 21 2021
AZZ008-037-211945-
Yavapai County Valleys and Basins-Yavapai County Mountains-
1203 PM MST Wed Jul 21 2021
...STRONG THUNDERSTORM NEAR KIRKLAND IN YAVAPAI COUNTY UNTIL 1245 PM
MST...
At 1202 PM MST, Doppler radar was tracking a strong thunderstorm near
Kirkland, or 23 miles southwest of Prescott Valley. This storm was
nearly stationary.
Pea size hail and winds in excess of 40 mph will be possible with
this storm.
Locations impacted include...
Peeples Valley and Kirkland.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 3443 11289 3449 11277 3448 11264 3429 11260
3425 11281
TIME...MOT...LOC 1902Z 341DEG 0KT 3435 11272
ELThe Flagstaff radar (KFSX), 115 km away, was scanning. The volume nearest the first event began at 19:32 UTC.
7 flash flood. Local standard time, as filed.
Water was flowing and estimated two feet deep over Stagecoach Road where it crosses Groom Creek.
The wash along Paradise Road flooded.
Social media post indicated road flooding in Fort Defiance.
The river gauge on the Agua Fria River near Humboldt measured a 6 foot rise.
Lewis Street in Williams was flooded.
The Bright Angel Trail in the Grand Canyon was washed out by a flash flood.
Havasu Creek at Supai rose 18 inches in about an hour. It took six hours for the creek to return to normal.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2021Every state in 2021This day in weather historyWarnings in Arizona, July 2021
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: 978769, 978774, 979008, 978767, 978773, 978777, 978776.