Strong high pressure centered over the Great Basin resulted in temperatures climbing above normal during the first part of September. According to the Maricopa County Department of Public Health, 15 heat-associated deaths occurred during this time.
Every event with a place to put it; 11 filed by county or forecast zone are drawn at its center, in a lighter ring. 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.
Strong high pressure centered over the Great Basin resulted in temperatures climbing above normal during the first part of September. According to the Maricopa County Department of Public Health, 15 heat-associated deaths occurred during this time.
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 Sep 4, 4:56 PM MST, 4 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 456 PM MST Sat Sep 4 2021 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Mostly dry conditions will prevail through the first part of next week with just a slight chance of thunderstorms over the mountains of eastern Arizona. Locally gusty winds and some dust are possible for brief periods in lower elevation communities of south-central Arizona. Otherwise towards the second half of next week, modest rain chances will return for most locations. Temperatures will remain near normal for most of next week. && .DISCUSSION... The most evident feature on early afternoon satellite imagery is a massive cyclonic circulation/easterly wave passing over the southern Baja. Organized convective systems have added individual vorticity centers within the larger circulation; and the trailing arm of one wing of vorticity and upper level shear axis was aiding in ascent over higher terrain areas of western NM/eastern AZ. However, 12Z sounding data sampled an increasing amount of dry air enveloping the boundary layer such that 8-9 g/kg mixing ratios will be common by this afternoon precluding any persistent deep convection beyond terrain initiation points. At best, a few residual showers/storm may clip through far eastern Gila County as NBM POPs only register in a 10-15% range. Many CAMs indicate a robust Gulf of California moisture push late this evening which will eventually aid in overall instability growth tomorrow. HREF membership suggests deep convective development over SE Arizona with semi-organized outflow boundaries propagating towards the forecast area. NBM POPs are no greater than 20% and focused along the southeast CWA border while HREF probabilities indicate about a 40% chance of outflow wind gusts greater than 30 mph. Thus based on model probabilistic output, impacts would primarily be limited to the potential for some localized dense blowing dust in Pinal Co. For Monday-Tuesday, the anticyclone to our north continues to build, with central heights attaining 99th percentile values. We will be on the edge of the high, which will mean persistent northeasterly flow (keeping moisture generally restricted to the south/east of our CWA) and near normal temperatures. With continued convective activity across Sonora, there will be the potential each night for gulf surges into our Western CWA (gusty windy, increased humidity, possibly lowered visibility due to lofted dust). By midweek, the anticyclone will roll east and develop a more southerly flow across our CWA. There is a consistent signal in EPS/GEFS/CMC members of some energy moving north into AZ/CA/NV within a weakness of the ridge. Low end (5-20%) NBM PoPs are spread through this period. One thing to watch is an area of potential TC development off the west central Mexican coast (currently a 50% probability of development from NHC). Some EPS and GEFS members do develop this system and move it west of the Baja peninsula. The implication here would be potential increased moisture levels into our western CWA. A couple of EPS/GEFS members are indicating some heavier rain is possible toward the end of the week. For now, QPF amounts do not seem very high with 95th percentile PQPF values around 0.25-0.50 inches. The increase in clouds and moisture should reduce temperatures a few degrees by the end of the week. && .AVIATION...Updated at 2355z South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Terminal area winds are fairly light, AOB 8 kts, with WSW winds continuing well into the evening hours. The overnight easterly switch may occur a few hours later than usual for Sky Harbor. Otherwise, the typical diurnal trend is expected to occur again tomorrow. Thunderstorms will stay well to the east this afternoon with no threat for outflows. Storms on Sunday will remain east of the terminal area may become close enough to pose a low threat for outflows Sunday evening (chances 10%). Southeast California/Southwest Arizona including KIPL and KBLH: There are no aviation weather concerns with fairly light winds AOB 8 kts while directions follow typical diurnal trends. Extended periods of light and variable winds are also likely to occur. && .FIRE WEATHER... Monday through Friday: Little chance of rain to start the period, but low end (10-20%) will spread across the region Wednesday through Friday. Humidity values will trend up slightly with temperatures holding steady or dropping slightly (especially toward the end of the week). Winds will generally follow diurnal trends aside from stronger gusts in thunderstorm outflows. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...18/Iniguez AVIATION...12 FIRE WEATHER...Iniguez
The national radar mosaic for the moment the first event began.
11 heat. Local standard time, as filed.
Two indirect fatalities were reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
Two fatalities (1 direct and 1 indirect) were reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
Two indirect fatalities were reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One indirect fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One indirect fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
Two indirect fatalities were reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One indirect fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances, and exact location unavailable.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Heat, Central Phoenix | 2021-09-04 | Unknown | Indirect | ||
| Heat, Central Phoenix | 2021-09-04 | Unknown | Indirect | ||
| Heat, Central Phoenix | 2021-09-05 | Unknown | Direct | ||
| Heat, Central Phoenix | 2021-09-05 | Unknown | Indirect | ||
| Heat, Northwest Valley | 2021-09-05 | Unknown | Indirect | ||
| Heat, Northwest Valley | 2021-09-05 | Unknown | Indirect | ||
| Heat, North Phoenix/Glendale | 2021-09-05 | Unknown | Indirect | ||
| Heat, East Valley | 2021-09-05 | Unknown | Indirect | ||
| Heat, Buckeye/Avondale | 2021-09-05 | Unknown | Direct | ||
| Heat, Central Phoenix | 2021-09-06 | Unknown | Indirect | ||
| Heat, Central Phoenix | 2021-09-06 | Unknown | Indirect | ||
| Heat, East Valley | 2021-09-06 | Unknown | Indirect | ||
| Heat, Central Phoenix | 2021-09-07 | Unknown | Direct | ||
| Heat, East Valley | 2021-09-07 | Unknown | Direct | ||
| Heat, Buckeye/Avondale | 2021-09-08 | Unknown | Direct |
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, September 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: 1077498, 1077499, 1077502, 1077503, 1077504, 1077505, 1077500, 1077507, 1077501, 1077509, 1077510.