As the region transitioned out of the monsoon, a compact low created a high shear - modest CAPE environment. Parameters were sufficient for supercell development and a few supercells did develop amongst isolated to scattered storms in the afternoon across South-central Arizona, including a right-mover that pushed into Phoenix and a left split.
Every event with a place to put it. Tap one for its entry below.
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.
As the region transitioned out of the monsoon, a compact low created a high shear - modest CAPE environment. Parameters were sufficient for supercell development and a few supercells did develop amongst isolated to scattered storms in the afternoon across South-central Arizona, including a right-mover that pushed into Phoenix and a left split. The environment was supportive of severe to large hail with lower freezing levels and steep mid-level lapse rates. Measured hail stones up to 1.0 to 1.5 diameter was observed with the few supercells. Most other storms also produced smaller hail throughout the day. Damaging winds and isolated flash flooding was also observed through the afternoon.
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 Oct 5, 4:46 AM MST, 7 hours 14 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 446 AM MST Tue Oct 5 2021 .UPDATE... Aviation discussion update. && .SYNOPSIS... A low pressure system will move through the Southwest today. Periods of showers and thunderstorms will continue this morning, then gradually end from west to east this afternoon and evening. Some storms across central Arizona could be strong this afternoon, capable of producing strong, damaging winds and large hail. Some blowing dust will also be possible. Dry weather returns tomorrow and Thursday with near normal temperatures. A low end rain chance is possible with another passing system Friday and Saturday with slightly cooler temperatures. A quiet weekend with typical temperatures is expect, with the potential for a dry but notably cooler and winder weather system next week. && DISCUSSION... An upper level low is just southwest of San Diego, where it has been generating extensive thunderstorm activity. Across our CWA, the forecast has generally been holding as we remain in the warm sector of the system. Moisture levels have been gradually increasing, leading to areas of showers developing mainly across our eastern CWA. Satellite-derived and objective analysis PWAT values show a tongue of 1"+ values with the axis over western Maricopa County, coincident with the ongoing showers. Per similar analysis, the western CWA is in a bit of a dry slot and at this point may not see much precipitation until the main low moves in within the next few hours. For Maricopa County and points east, showers with embedded "garden variety" thunderstorms will continue for a few hours this morning. SPC mesoanalysis does show ~1000 J/kg of DCAPE, so even though the showers/thunderstorms likely won't be very strong themselves, the environment remains conducive to gusty outflow winds. Rainfall amounts thus far have been light, where it has rained, at about 0.1-0.2", but continual training in some areas will push this amounts higher. It does look like there will be a notable break across central Arizona later this morning, with even quite a bit of sun which coupled with the on-going WAA will help push temperatures toward 90°F. The main show will be the passage of the filling but still potent low as it moves northeast across the Colorado River basin. Latest CAMs are in pretty good agreement on overall convective trends, which is not a surprise given the robust synoptic forcing in place. Uncertainty hinges on the exact track of the low. Thunderstorms will likely develop across the Imperial Valley around 12Z, give or take an hour, and move to the northeast. Instability will be a bit limited, perhaps around 500 J/kg, which coupled with the strong PVA will support a few strong (but likely sub-severe) thunderstorms. Downburst/outflow winds could approach 50 mph. As the storms and parent low move into southwest Arizona (heading for northern Arizona) this afternoon, the environment becomes more favorable for severe weather. HREF mean MUCAPE values reach 500-1000+ J/kg across Yuma/La Paz/Maricopa Counties during the afternoon hours. Bulk shear vectors approach 50 kt. Storm updrafts could intensify with the instability and begin rotating given the shear, possible reaching severe limits with respect to straight line winds (58+ mph) and hail (1"+). The latest SPC outlook supports this with a 5% hail and wind contour. Notably there is a 2% tornado contour just to the north of our CWA - a tornado or two can't be ruled out with these storms, especially across northern Maricopa County where increasing terrain height will support lower LCLs. It should also be noted the potential for no convection across the Phoenix area, despite the instability and shear, should the low track further north. Today certainly has boom-bust potential. QPF values have not change much, with deterministic amounts (storm total) for lower elevations around 0.1-0.2" (10/90th percentile of 0.0/0.4-1.2"). and higher elevations near 0.2-0.4" (10/90th percentile 0.1/2.0"). The higher ends represent potential associated with strong thunderstorms and/or training of heavy showers for extended periods. Overall it appears any flooding threat is minimal with exception of burn scars and downstream areas. The thunderstorm and severe threat will very quickly diminish this afternoon/evening, from west to east, as the vort max ejects towards the Four Corners. A few residual showers will be possible Wednesday, mainly near elevated terrain locations, but otherwise it will be a quiet day. Global ensemble members still indicate another short wave approaching from the northwest Thursday/Friday, but due to a strong anticyclone centered over Texas will not progress much toward our CWA. Instead, an unusually strong SW-NE oriented jet streak will develop (120+ kt, 99th percentile) across the Southwest. The embedded shortwave and jet dynamics will bring slightly cooler temperatures, afternoon breezes, and may generate a few showers across Arizona. Temperatures will dip a bit behind the system for Friday/Saturday before bouncing back Sunday/Monday ahead of the next system. Cluster scenarios indicate another, potentially deeper, trough early next week (Mon/Tue). While there are typical depth/timing differences on the specifics, there is markedly less spread than seen the previous few days, with the vast majority of EPS/GEM/GEFS members resolving the trough. It appears it will be dry for our area (very few members show any rain at all), but there will be a period of enhanced winds with its passage. It will also get much cooler in this scenario - the current deterministic forecast has Wednesday morning lows in the lower 40s to lower 50s. && .AVIATION...Updated at 1145Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Showers will fill in across the Phoenix area for the next few hours. Included tempo TS in TAFs given scattered nature of embedded convection and modest ceiling reductions, but not winds at this time as the thunderstorms are not particularly strong. Expecting a window of improved conditions later this morning and into the very early afternoon. Then arrives a window of several hours where stronger thunderstorms will be possible across the Phoenix area. Development and coverage is still uncertain but enough potential to continue PROB30 groups. Should they develop, the storms will be fairly progressive and not linger for long. Clouds will quickly clear behind the storms this evening. Winds will show atypical patterns through the day, with easterly flow taking hold later tonight. Southeast California/Southwest Arizona including KIPL and KBLH: Scattered showers will continue for several hours across the region, with an area of thunderstorms currently in the Imperial Valley gradually moving to the northeast. Gusty winds will be possible with the thunderstorms along with MVFR conditions (due to rain, some blowing dust, and/or reduced ceilings). Quickly improving weather this afternoon as the storms move to the east. Winds will show atypical patterns through the morning and afternoon, with preferred drainage directions taking hold later this evening. && .FIRE WEATHER... Thursday through Monday: One weather system will move through the region Thursday and Friday, bringing low end rain chances and a slight uptick in afternoon humidity. Slightly cooler and drier weather arrives Saturday, but warmer and drier weather is expected Sunday and Monday. Overnight humidity values will generally be trending down through the entire period. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...Iniguez AVIATION...Iniguez FIRE WEATHER...Iniguez
Special Weather Statement
National Weather Service Phoenix AZ
1106 AM MST Tue Oct 5 2021
AZZ534-538-051830-
Aguila Valley AZ-Tonopah Desert AZ-
1106 AM MST Tue Oct 5 2021
...Strong thunderstorms will impact portions of Maricopa County
through 1130 AM MST...
At 1106 AM MST, Doppler radar was tracking strong thunderstorms along
a line extending from near Aguila to 15 miles north of Tonopah.
Movement was north at 35 mph.
HAZARD...Winds in excess of 40 mph and penny 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...
Aguila.
This includes US Highway 60 between mile markers 82 and 106.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
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.
&&
LAT...LON 3392 11277 3361 11300 3379 11317 3399 11323
3400 11323 3400 11282
TIME...MOT...LOC 1806Z 190DEG 29KT 3399 11315 3371 11301
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
1116 AM MST Tue Oct 5 2021
AZZ540-550-553-554-559-051845-
South Mountain/Ahwatukee AZ-Sonoran Desert Natl Monument AZ-
Buckeye/Avondale AZ-Northwest Pinal County AZ-West Pinal County AZ-
1116 AM MST Tue Oct 5 2021
...A strong thunderstorm will impact portions of Maricopa and Pinal
Counties through 1145 AM MST...
At 1116 AM MST, Doppler radar was tracking a strong thunderstorm near
Estrella Sailport, or 22 miles south of Avondale, moving north at 30
mph.
HAZARD...Winds in excess of 40 mph and half inch 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...
Avondale, Goodyear, Estrella Sailport, Estrella Mountain Park,
Rainbow Valley, Komatke and Mobile.
This includes AZ Route 238 between mile markers 25 and 38.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
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 3336 11212 3335 11210 3302 11215 3302 11237
3337 11242
TIME...MOT...LOC 1816Z 177DEG 26KT 3310 11227
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
1137 AM MST Tue Oct 5 2021
AZZ531-536-051900-
Gila River Valley AZ-Kofa AZ-
1137 AM MST Tue Oct 5 2021
...A strong thunderstorm will impact portions of east central Yuma
County through NOON MST...
At 1137 AM MST, Doppler radar was tracking a strong thunderstorm over
Dateland, or 49 miles northwest of Ajo, moving north at 35 mph.
HAZARD...Winds in excess of 40 mph and half inch 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...
Dateland and Paloma.
This includes AZ Interstate 8 between mile markers 60 and 75.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 3271 11344 3271 11366 3308 11371 3308 11334
TIME...MOT...LOC 1837Z 183DEG 32KT 3279 11356
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
1142 AM MST Tue Oct 5 2021
AZZ537-541-051915-
Cave Creek/New River AZ-Northwest Valley AZ-
1142 AM MST Tue Oct 5 2021
...A strong thunderstorm will impact portions of Maricopa County
through 1215 PM MST...
At 1142 AM MST, Doppler radar was tracking a strong thunderstorm near
Beardsley, or near Sun City West, moving north at 40 mph.
HAZARD...Winds in excess of 40 mph and penny 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...
Surprise, El Mirage, Wittmann, Sun City West, Surprise Stadium, Lake
Pleasant, Beardsley and Vistancia.
This includes the following highways...
US Highway 60 between mile markers 129 and 145.
AZ Route 74 between mile markers 6 and 21.
AZ Route 303 between mile markers 114 and 127.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 3389 11231 3389 11228 3391 11225 3371 11231
3359 11232 3361 11252 3395 11255
TIME...MOT...LOC 1842Z 183DEG 33KT 3367 11244
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
1143 AM MST Tue Oct 5 2021
AZZ537-540-543-544-550-553-559-051915-
South Mountain/Ahwatukee AZ-Sonoran Desert Natl Monument AZ-
Buckeye/Avondale AZ-Northwest Pinal County AZ-Central Phoenix AZ-
Northwest Valley AZ-North Phoenix/Glendale AZ-
1143 AM MST Tue Oct 5 2021
...A strong thunderstorm will impact portions of Maricopa and Pinal
Counties through 1215 PM MST...
At 1143 AM MST, Doppler radar was tracking a strong thunderstorm near
Phoenix International Raceway, or 8 miles southwest of Laveen, moving
north at 40 mph.
HAZARD...Winds in excess of 40 mph and penny 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...
Phoenix, Glendale, Avondale, Goodyear, El Mirage, Tolleson,
Youngtown, Waddell, Laveen, Cashion, Sun City, Litchfield Park, North
Mountain Park, South Phoenix, Arizona State Fairgrounds, Downtown
Peoria, Downtown Glendale, Estrella Mountain Park, Glendale Sports
Complex and Luke AFB.
This includes the following highways...
AZ Interstate 10 between mile markers 128 and 146.
AZ Interstate 17 between mile markers 196 and 209.
AZ Route 51 between mile markers 5 and 7.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
A Severe Thunderstorm Watch remains in effect until 800 PM MST for
south central and southeastern Arizona.
&&
LAT...LON 3322 11211 3323 11236 3360 11238 3359 11203
TIME...MOT...LOC 1843Z 183DEG 33KT 3332 11222
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH
SDBSpecial Weather Statement
National Weather Service Phoenix AZ
1151 AM MST Tue Oct 5 2021
AZZ541-546>549-551-051915-
Fountain Hills/East Mesa AZ-Scottsdale/Paradise Valley AZ-
Cave Creek/New River AZ-East Valley AZ-
Southeast Valley/Queen Creek AZ-Rio Verde/Salt River AZ-
1151 AM MST Tue Oct 5 2021
...A strong thunderstorm will impact portions of Maricopa County
through 1215 PM MST...
At 1151 AM MST, Doppler radar was tracking a strong thunderstorm over
Freestone Park, or over Mesa, moving north at 40 mph.
HAZARD...Winds in excess of 40 mph and penny 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...
Mesa, Chandler, Scottsdale, Gilbert, Fountain Hills, East Mesa, Mesa
Riverview Mall, Granite Reef Dam, Gilbert City Hall, Falcon Field
Airport, McDowell Mountain Park, Salt River Indian Community,
Downtown Mesa, Usery Mountain Park, Superstition Springs Mall, San
Tan Village Mall, Freestone Park, Goldfield Ranch, Fiesta Mall and
Phoenix Mesa Gateway Airport.
This includes the following highways...
US Highway 60 between mile markers 177 and 191.
AZ Route 87 between mile markers 167 and 198.
AZ Route 202 between mile markers 11 and 33, and between mile markers
35 and 41.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
A Severe Thunderstorm Watch remains in effect until 800 PM MST for
south central Arizona.
&&
LAT...LON 3372 11154 3329 11166 3331 11188 3363 11190
3363 11187 3366 11190 3376 11191
TIME...MOT...LOC 1851Z 183DEG 33KT 3339 11177
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH
SDBThe Phoenix radar (KIWA), 16 km away, was scanning. The volume nearest the first event began at 18:57 UTC.
15 hail, 3 thunderstorm wind, 2 flash flood. Local standard time, as filed.
Images on social media showed accumulating hail with the larges stones estimated up to nickel size.
Social media photos show hail stones up to nickel-sized. Time estimated from radar.
Salt River Project EM reported 3 wooden power poles were broken near the Spurlock substation, causing power outages. Wind speeds estimated around 60 mph. Time estimated from radar. No injuries were reported. Full extent of damage not provided.
Mesonet station SRP45 measured a 73 mph wind gust.
Social media video showed swift-moving water within Weekes Wash and flowing across State Route 88 near 1st Water Road, making the road impassable. Timing approximated. No damages or injuries were reported.
Mesonet station AU919 (2 SSE Roosevelt) measured a 63 mph wind gust.
Arizona Department of Transportation reported State Route 188 was closed between mile post 251 and 255 due to a mudslide. Photos show 4 to 6 feet of mud across the highway near mile post 253 that had to be cleared with heavy machinery. Flow originated from a portion of the 2020 Bush fire burn scar. NWS Phoenix in collaboration with Arizona Geological Survey declared the mudslide a hyperconcentrated flow and therefore entered as a flash flood. Timing estimated from radar. No damage or injuries were reported.
Observer at Gila Bend Airfield reported 1 inch diameter hail in the METAR.
Chaser estimated golf ball sized hail fell near Riggs Road and Bullard Avenue in Rainbow Valley. No damages reported. Time estimated from radar.
Storm chaser reported estimated 1 inch diameter hail while driving on Loop-202.
Hail just less than 1 inch in diameter fell for roughly 10 minutes based on a social media report.
Social media photo of a 1 inch diameter hail stone.
Social media video shows hail falling in Hermoso Park. Largest stones estimated at 1.25 inches in diameter.
Social media photo of an estimated 1.5 inch in diameter hail stone. Hail reportedly fell for around 5 minutes.
Social media video showing a collection of hail with the largest stones estimated around 1 inch in diameter.
Social media photo of hail stones estimated up to 1.25 inches in diameter.
Multiple videos from Phoenix Sky Harbor Airport showing hail falling with sizes estimated around pea to penny.
Social media photo of estimated nickel-sized hail.
Social media video of estimated penny-sized hail falling.
Social media video of estimated penny-sized hail.
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, October 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: 990375, 990419, 990404, 990408, 990414, 990409, 990418, 990376, 990379, 990382, 990383, 990384, 990385, 990386, 990387, 990388, 990389, 990390, 990391, 990392.