Strong high pressure centered over the Great Basin and an inverted trough near the Arizona/Mexico international border promoted enhanced east/northeast steering flow favorable for maintaining thunderstorms off the high terrain into the lower elevations. A very moist and unstable atmosphere promoted the development of strong to severe thunderstorms that pushed off the high terrain of southern…
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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.
Strong high pressure centered over the Great Basin and an inverted trough near the Arizona/Mexico international border promoted enhanced east/northeast steering flow favorable for maintaining thunderstorms off the high terrain into the lower elevations. A very moist and unstable atmosphere promoted the development of strong to severe thunderstorms that pushed off the high terrain of southern Gila County and into the lower deserts during the evening of the 15th. Several instances of damage were reported, which included multiple downed trees in the Mesa area. 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 Aug 15, 4:59 PM MST, 4 hours 36 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 459 PM MST Sun Aug 15 2021 .UPDATE... Updated 00Z aviation discussion. && .SYNOPSIS... Abundant monsoon moisture will remain entrenched across the Desert Southwest into the middle part of the week maintaining daily chances for showers and thunderstorms. The primary threats with any storms will be localized heavy rainfall that may cause flash flooding. Localized strong winds and some blowing dust will also be possible for desert locations. A gradual decrease in moisture during the latter half of the week should reduce rain chances across the lower deserts as early as Thursday night. Temperatures will remain below normal for most of Arizona, while near normal temperatures are mostly expected for southeast California. && An anomalously moist airmass continues to dominate the region today. This morning's PSR 12Z sounding registered an anomalously high PW of 2.19" and mean W of 16.5 gm/kg. The objective analysis shows the UL high centered over the NE CA/NW NV border with pronounced mid level ENE flow along its S flank which is introducing some moderate mid level drying, with an area of mid-level elevated mean RH sliding into S AZ/N MX. Vort max's and inverted troughs are over this same borderland NW MX/N Baja area with an additional connected trough over NW Chihuahua/SSW NM. The disturbances were supporting a small area of rain/showers over Imperial Cty and modest isolated thunderstorms over S-SE AZ. On the NE flank of the high was another shortwave trough pushing SSEwrd into N CO/N UT. An area of isolated thunderstorms was developing ahead of this trough in N AZ and CO. The midday ACARs mean sounding confirmed some pronounced mid level drying centered at H5 with PW down to 1.11", although elevated lower mid level and BL moisture were still supporting SB-MU CAPE in the low 1000s with modest CIN. The slight-moderate instability was held in check with a strong CAP just below H7. Early afternoon METSAT showed decreasing cloudiness with partly- mostly sunny conditions across much of the deserts with mostly fair weather CU. The HREF members are in much better agreement for this afternoon and evening's storm prospects. They are picking up on the short term drying and decreasing instability trend by agreeing on keeping storms rather isolated this afternoon and evening and confined mainly to the high terrain of N-E AZ, due to the approaching shortwave to the N, and the deserts of S-SE AZ due to the inverted troughs. The NBM has also locked onto the trend as well with only 10-20% POPs depicted for this afternoon and into Monday. Some isolated storms to the north may try to impact the far N portions of La Paz Cty from near Parker to Alamo Lake/State Park. Any isolated thunderstorms that manage to form later today will still be capable of producing localized flash flooding across the deserts or near Phoenix due to the wet soils. Beginning later tomorrow and through the middle of the week the shortwave trough and associated vort max's up north will push Swrd into NM and E-AZ as PW once again recovers and inversion CAPS are weakened through the column. The HREF members are now fairly bullish on either a scattered, or scattered to numerous, line of organized thunderstorms forming along the Rim on Monday afternoon and descending S into Phoenix and the lower deserts Monday evening. These storms will be capable of producing strong winds, heavy rainfall, and localized flooding as potential threats. HREF also calls for a >70% chance of 35 mph wind gusts Monday evening in and around Phoenix. In preparation for this system the Flash Flood Watch for S-Cent AZ has been extended through 2 AM MST on Monday night. The active weather pattern should continue into at least Wednesday as the inverted trough that will exit to our southwest today, likely comes back around into our region on Wednesday. This weak cut off low (what was the inverted trough) looks to get picked up in the flow as an anomalously strong trough dives through the Pacific Northwest into the Great Basin. There is good model evidence of a fairly strong upper level jet entering Arizona from the south Tuesday night into early Wednesday while there may also be increasing jet forced ascent from the trough diving into the Great Basin. With plenty of moisture likely still in place across our region, Tuesday night into Wednesday could end up being another fairly widespread (modest) rain event across south-central and eastern Arizona. For the late week and weekend model uncertainty increases, but the majority of the ensembles show the deep trough to our north and then to our northeast becoming the dominant feature. With broad troughing likely taking over our region, we should be under a drying westerly flow by Thursday, likely lasting through next weekend. Models are in better agreement showing this drier air working into our region Thursday into Friday, likely ending or significantly reducing our rain chances over the lower deserts on Thursday with only very limited rain chances over the Arizona high terrain. Temperatures this week are likely to be fairly stable with the western deserts mostly around seasonal normals each day. For the south-central Arizona deserts, including the Phoenix area, below normal temperatures are likely to continue with highs mostly in the mid 90s to around 100 degrees. && .AVIATION...Updated at 2359Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Aside from a 20% chance of convective outflows this evening, minimal aviation impacts are expected until early Monday evening when another round of strong to severe thunderstorms are possible. Light and variable or south-southwest winds below 10 knots will persist at the Phoenix TAF sites until easterly flow returns around 05-06Z. There is only about a 10% chance of storms at any terminal tonight if any weak northeasterly outflows push into the lower deserts due to a low-level stable layer. Westerly flow should return by late Monday morning through the afternoon hours, with a 40% chance of strong to severe thunderstorms during the evening. The best timing of outflows and storms is between 01-04Z Tuesday, with a 70% chance of winds exceeding 35 knots and at least a 10% chance of winds exceeding 50 knots. BKN-OVC ceilings in these storms should generally remain above 6-8 kft. Southeast California/Southwest Arizona including KIPL and KBLH: Minimal aviation concerns are expected through Monday morning, with gusty south-southeast winds expected on Monday afternoon. Winds will generally favor a southeast component at KIPL with speeds generally remaining below 10 knots aside from gusts up to 20 knots on Monday afternoon. At KBLH, winds will generally favor a southeast to southerly component with speeds below 10 knots aside from gusts up to 25 knots on Monday afternoon. FEW-SCT ceilings should remain above 10 kft. && .FIRE WEATHER... Tuesday through Saturday: Elevated moisture levels and a threat of showers and thunderstorms will continue through at least Wednesday. A drying trend should then set in late in the week with dwindling chances for wetting rains on Thursday and likely little if any rain chances by Friday. The strongest storms early in the week will be capable of producing localized flash flooding, particularly in the higher terrain north and east of Phoenix. Minimum humidities mostly between 30-45% early in the period will gradually lower to 20-30% late in the period. Temperatures will remain below normal across much of Arizona through the period, while the western deserts see near normal readings. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Flash Flood Watch through late Monday night for AZZ534-537>563. CA...None. && DISCUSSION...Sawtelle/Kuhlman AVIATION...Hopper FIRE WEATHER...Kuhlman
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
604 PM MST SUN AUG 15 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0241 AM FLASH FLOOD 1 E AVONDALE 33.44N 112.33W
08/14/2021 MARICOPA AZ MESONET
CORRECTS PREVIOUS TSTM WND DMG REPORT FROM 1
E AVONDALE. **DELAYED REPORT** COUNTY FLOOD
GAGE AT BUCKEYE RD/AGUA FRIA RIVER EXCEEDED
ALARM STAGE (0.72 FT) REACHING 0.79 FT AT
1932 CFS. FLOWING WATER LEAD TO CLOSURE OF
LOWER BUCKEYE RD, ONE MILE SOUTH OF THE
GAGE, BETWEEN 4TH ST AND 127TH AVE.
&&
ADPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
610 PM MST SUN AUG 15 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1050 PM HEAVY RAIN 4 SE DEER VALLEY 33.63N 112.07W
08/13/2021 E2.50 INCH MARICOPA AZ PUBLIC
***DELAYED REPORT*** HEAVY RAIN LED TO A
PARTIAL ROOF COLLAPSE AT MOON VALLEY BIBLE
CHURCH. NO INJURIES WERE REPORTED. TIME
ESTIMATED FROM HEAVIEST RAINFALL AND
RAINFALL ESTIMATED FROM RADAR AND NEARBY
MESONET OBSERVATIONS.
&&
SDBPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
640 PM MST SUN AUG 15 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0645 PM TSTM WND DMG 4 NW EAST MESA 33.46N 111.72W
08/11/2021 MARICOPA AZ TRAINED SPOTTER
**DELAYED REPORT** FLIPPED OVER PLANE AND
SHEET ROOFING DAMAGE FROM THUNDERSTORM WIND
GUSTS REPORTED. DAMAGE WAS CORROBORATED VIA
PILOT-TO-TOWER AUDIO COMMUNICATION.
&&
ADPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
654 PM MST SUN AUG 15 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1055 PM TSTM WND DMG 3 E EAST MESA 33.42N 111.63W
08/13/2021 MARICOPA AZ PUBLIC
***DELAYED REPORT*** 40 FOOT TREE FELL
THROUGH A 5 FOOT CINDERBLOCK WALL AND ONTO A
CHICKEN COOP. NO INJURIES REPORTED. WINDS
ESTIMATED 55 TO 65 MPH. TIME ESTIMATED FROM
RADAR.
&&
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
749 PM MST Sun Aug 15 2021
AZZ560-563-160345-
Southeast Gila County AZ-San Carlos AZ-
749 PM MST Sun Aug 15 2021
...Strong thunderstorms will impact portions of Gila County through
845 PM MST...
At 749 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from 8 miles south of Cedar Creek to 12 miles
southwest of Fort Apache to 15 miles south of Seven Mile. Movement
was west at 25 mph.
HAZARD...Wind gusts of 50 to 55 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Hilltop and Sawmill.
This includes US Highway 60 between mile markers 269 and 297.
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.
Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
These storms 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 3347 11017 3344 11020 3344 11032 3340 11035
3340 11042 3354 11064 3379 11069 3381 11066
3383 11032 3360 11004 3360 10999 3347 11000
TIME...MOT...LOC 0249Z 077DEG 21KT 3377 11014 3365 11012 3357 11001
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...55 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
918 PM MST Sun Aug 15 2021
AZZ552-558-560>563-160500-
Southeast Gila County AZ-San Carlos AZ-Dripping Springs AZ-
Globe/Miami AZ-Superior AZ-Pinal/Superstition Mountains AZ-
918 PM MST Sun Aug 15 2021
...A strong thunderstorm will impact portions of Gila and Pinal
Counties through 1000 PM MST...
At 917 PM MST, Doppler radar was tracking a strong thunderstorm near
Cutter, or near Globe, moving southwest at 25 mph.
HAZARD...Wind gusts of 50 to 55 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Globe, Superior, Miami, Cutter, Central Heights-Midland City,
Top-Of-The-World and Claypool.
This includes the following highways...
US Highway 60 between mile markers 225 and 245, and between mile
markers 248 and 256.
AZ Route 70 between mile markers 253 and 268.
AZ Route 77 between mile markers 152 and 170.
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.
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 3328 11049 3312 11077 3310 11086 3324 11094
3316 11106 3316 11108 3332 11115 3348 11061
TIME...MOT...LOC 0417Z 066DEG 23KT 3333 11072
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...55 MPH
SDBThe Phoenix radar (KIWA), 72 km away, was scanning. The volume nearest the first event began at 04:36 UTC.
5 thunderstorm wind, 1 hail. Local standard time, as filed.
Damaging wind gusts moving through the Roosevelt Lake area resulted in a metal carport roof being blown off. Wind gusts estimated to be between 50-60 mph. No injuries were reported.
Estimated pea-sized hail fell for approximately one hour and caused significant crop damage around the property of Reevis Mountain School. Most of the fruit trees were affected, with the peach and jujube harvests deemed total losses. Nearly an acre of vegetable leaves were shredded. Many of the walnuts and all pecans fell off their trees. Damage costs were not provided.
A picture on social media showed a large pine tree down at an apartment complex near McKellips Road and Higley Road in Mesa. Wind estimated to be between 50-60 mph based on nearby observations and radar. No injuries were reported.
A large pine tree approximately 2-3 feet in diameter fell on top of a garage and a vehicle near University Drive and Greenfield Road in Mesa. No injuries were reported. Timing was estimated using radar.
Multiple large pine trees and power poles were blown down at an apartment complex along University Drive between Val Vista Drive and Lindsay Road. Additional downed trees were reported in this area. No injuries were reported. Timing was estimated using radar.
Photos on social media showed several large trees down along with damage to a playground in an area near Arizona Avenue between Elliot Road and Warner Road. A large tree estimated to be approximately 2-3 feet in diameter was uprooted at an apartment complex at Warner Road and Evergreen Street. No 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, August 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: 983476, 986973, 983613, 983478, 983480, 983851.