An anomalously moist environment combined with weak upper level forcing mechanisms allowed for showers to develop across parts of south-central Arizona on the 24th with some showers producing locally heavy rainfall. One of these heavier showers developed over the recent Telegraph burn scar and produced upwards of around an inch of rain.
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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 PSR wrote it up.
An anomalously moist environment combined with weak upper level forcing mechanisms allowed for showers to develop across parts of south-central Arizona on the 24th with some showers producing locally heavy rainfall. One of these heavier showers developed over the recent Telegraph burn scar and produced upwards of around an inch of rain. A nearby trained weather spotter in the Claypool area reported approximately 1.2 of rain fell in about 30-35 minutes. The heavy rainfall over the burn scar led to enhanced runoff that resulted in flash flooding occurring in Ice House Canyon. No injuries were reported.
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 Phoenix, AZ wrote its last area forecast discussion before the first event at Jul 24, 12:45 PM MST, 1 hour 30 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 1245 PM MST Sat Jul 24 2021 .UPDATE...Updated 18Z Aviation. && .SYNOPSIS... A low pressure system will continue to drift slowly towards Arizona. With abundant Monsoon moisture in place, the threat of showers and thunderstorms will continue through Sunday. The strongest storms will be capable of producing heavy rainfall and areas of flash flooding. Temperatures will also be well below normal through early next week. Warmer and drier conditions are anticipated next week as the low pressure system lifts northward into the Great Basin. && .DISCUSSION... Closed low that is responsible for all of the recent rainfall is evident on water vapor imagery centered across central New Mexico and moving westward. On the ascending flank of the low, a vort lobe is providing the lift needed for another MCS across northeastern Arizona. Although the MCS has warmed and weakened over the past several hours, HREF consensus indicates additional convection will develop further south and generally across south-central Arizona early this morning. In addition to the vorticity-forced ascent, latest ACARS from Phoenix did indicate roughly 250-500 J/kg of MLCAPE. It is expected that storms will be favored in these areas. Latest runs of the HRRR continue to suggest only isolated activity will develop early this morning across the lower deserts of central Arizona. However, the FV3 stands out from the other HREF members and has captured the current setup quite well. It indicates isolated cells across central Arizona will increase in coverage early this morning, before shifting southward and dissipating later this morning. The official forecast largely based on the NBM generally reflects this scenario. Additional convection is possible this afternoon and evening, though the uncertainty in location/timing increases considerably based on the latest CAMs. Given the abundant low-level moisture, any storms that develop will be capable of producing heavy rainfall. Flash flooding remains the primary concern, particularly in areas where the ground is already saturated from Friday’s rainfall. CAMs indicate only very low probabilities of strong winds/blowing dust. After what was likely one of the coolest July afternoons of all- time in the Phoenix area Friday, well-below normal temperatures are anticipated again today. Forecast high is in the upper 80s, though the inter-quartile range depicted by the multi-model ensemble is nearly 10 degrees, meaning there is a wide range of possibilities depending on how the clouds/rainfall play out. The aforementioned closed low will weaken tonight while drifting westward into Arizona. With the loss of a closed circulation, it will technically become an inverted trough. A southeasterly flow will consequently develop across southern Arizona, still favorable for convection and areas of heavy rain. PoPs were again increased across the forecast area Sunday. Storms will even be possible across southeastern California, given the moist easterly flow. Ensembles remain in good agreement that warmer and drier conditions develop during the first half of the week as the inverted trough lifts out in the Great Basin. Driest day will likely be Monday. Thereafter, models depict a persistent easterly component to the steering flow with the Monsoon High situated well to our north. This will at least keep rain chances at or above climatology through the week. Latest NBM also indicates return to near normal temperatures is likely by the middle of the week. && .AVIATION...Updated at 1944Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Most shower activity has shifted out of the Phoenix metro area, aside from a few weak isolated showers. Models are not showing much in the way of showers or storms through the rest of the day, but given the environment isolated activity could still spring up at any time. Otherwise, CIGs and wind will be the primary aviation impacts. Model probabilities of CIGs less than 6 kft decrease to ~10% after 22-23Z. While FEW to SCT lower clouds may continue to linger through the day, show some improvement in CIGs beginning at 22Z. Winds are expected to favor the south to southeast through the afternoon with speeds around 10 kts or less. If conditions clear up enough, a brief westerly wind shift could occur this afternoon, but confidence is too low to include in the TAF. Better rain chances and thunderstorm chances are supported by HREF for late tonight/early tomorrow and tomorrow afternoon, respectively. Southeast California/Southwest Arizona including KIPL and KBLH: While a brief period of residual showers may affect KIPL during the next few hours, quiet weather with periodic thicker mod/high clouds will be more common. Additional showers are possible Sunday morning. Similar to the past several days, south to southeast winds will be preferred through the period. && .FIRE WEATHER... Monday through Friday: Storm activity takes a substantial trend downward during the first half of the week as an upper low exits the desert southwest and drier air moves into the region - though Monday may still be active over SE CA. The least active day looks to be Tuesday with storm chances confined to south-central Arizona. Accordingly, humidities trend downward with Min RH values decreasing to the 15-25% range on the lower deserts by Wednesday (25-35% higher terrain) with little change thereafter. Max RH values on the lower deserts decline to 25- 50% (lowest over SE CA) by Thursday morning (50-80% higher terrain). High temperatures start of several degrees below normal Monday and climb to normal readings over south-central AZ by Wednesday (2-4 degrees above normal SW AZ and SE CA). Little change thereafter. Apart from thunderstorms, winds will favor familiar diurnal patterns. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Flash Flood Watch through Sunday evening for AZZ534-537>563. CA...None. && DISCUSSION...Hirsch AVIATION...Benedict/18 FIRE WEATHER...AJ
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1254 PM MST SAT JUL 24 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0605 PM FLASH FLOOD 7 S NEW RIVER 33.81N 112.12W
07/23/2021 MARICOPA AZ DEPT OF HIGHWAYS
*** DELAYED REPORT *** MCDOT TWITTER REPORTS
ROAD CLOSURE OF 27TH AVE. FROM CLOUD RD. TO
DOLORES RD. DUE TO FLOODING.
0605 PM FLASH FLOOD 6 SSE NEW RIVER 33.84N 112.10W
07/23/2021 MARICOPA AZ DEPT OF HIGHWAYS
*** DELAYED REPORT *** MCDOT TWITTER REPORTS
19TH AVE. CLOSED FROM DESERT HILLS DR. TO
IRVINE RD. DUE TO FLOODING.
&&The Phoenix radar (KIWA), 83 km away, was scanning. The volume nearest the first event began at 21:15 UTC.
1 flash flood. Local standard time, as filed.
A video from social media showed swift moving water flowing down a creek in Ice House Canyon with known low water crossings along the creek. Timing was estimated from the video. No damage or injuries were reported.
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: 976250.