A broad upper level ridge over the Desert Southwest led to continued above normal temperatures along with excessive heat conditions for the middle part of September. Temperatures most afternoons during this time in Phoenix topped out around 108-109 degrees.
Every event with a place to put it; 27 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.
A broad upper level ridge over the Desert Southwest led to continued above normal temperatures along with excessive heat conditions for the middle part of September. Temperatures most afternoons during this time in Phoenix topped out around 108-109 degrees. According to the Maricopa County Department of Public Health, 10 heat-associated fatalities occurred during this time. One of these fatalities included a person who died while hiking in Scottsdale. According to local media reports, a couple from Rhode Island started hiking around noon on the 12th at Brown's Ranch Trailhead in Scottsdale. After splitting up during the hike, the wife never returned to their meeting location. Local authorities responded and discovered that the wife had succumbed to the heat.
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 10, 9:55 PM MST, 2 hours 5 minutes earlier.
Area Forecast Discussion
National Weather Service Phoenix AZ
955 PM MST Fri Sep 10 2021
.UPDATE...Updated Aviation discussion.
&&
.SYNOPSIS...
Unseasonably warm temperatures and dry conditions will prevail
through early next week as strong high pressure remains over the
region. High temperatures through Saturday will run 3 to 5 degrees
above normal before fairly widespread excessive heat with highs
between 107 to 112 degrees impacts the lower deserts on Sunday
and Monday. A gradual cooling trend is then expected during the
latter half of next week, but dry conditions will mostly likely
persist for the foreseeable future.
&&
.DISCUSSION...
Water vapor imagery shows a strong upper level high remains
centered over New Mexico with a fairly deep upper level trough
moving inland across northern California and Oregon. WV imagery
also shows some modest moisture transport from tropical storm
Olaf, but easterly flow on the south side of the high pressure
will push most of its moisture out into the Pacific. As the upper
level trough moves across the Great Basin today and tomorrow the
upper level ridge will be slightly depressed, which will allow
high temperatures to drop a few degrees, though still remaining
well above normal. Highs will mostly range from 104-108 degrees
across the south- central Arizona deserts to a degree or so warmer
over southwest Arizona and southeast California. Meanwhile,
lingering low level moisture around the outer fringes of the high
center (along with some minor advection from Olaf) should again be
just enough for a few isolated showers and thunderstorms across
southeast California and maybe southwest Arizona today. High- res
models mostly show a bit less convective activity than what
occurred on Thursday.
Excessive Heat conditions are likely to return for much of the
lower deserts by Sunday as the trough to our north exits well to
the northeast, while also allowing the ridge to elongate and
spread westward through southern California. The upper level ridge
center is also expected to shift over Arizona on Sunday. Upper
level heights will not increase too much, but there will be a net
warming of the column leading to a few degrees of warming at the
surface. Additionally, even drier conditions are anticipated
starting Sunday with afternoon surface dew points likely dropping
into the 40s, providing more optimal boundary layer heating
conditions. The NBM has been consistent in showing high
temperatures reaching between 107-112 degrees across the lower
deserts for both Sunday and Monday with Monday's readings around
one degree warmer than Sunday. The NBM probability of reaching 110
degrees in Phoenix for Sunday and Monday is slightly less than
yesterday, currently showing around 30%, while Monday shows a 15%
probability of reaching 112 degrees. Very similar to slightly
higher probabilities are also shown for Yuma and El Centro. Daily
record highs for Phoenix for Sunday and Monday are 110 and 109
degrees. Accordingly, heat records are likely to be threatened
both days. An excessive heat warning remains in effect for Sunday
and Monday over much of the forecast area to cover this period of
enhanced heat.
From Tuesday onwards uncertainty begins to grow, but there is a
general ensemble agreement that another trough will track
southeastward into the central rockies midweek. This trough
should help to depress heights aloft over our region. Some
cooling should be realized by Tuesday, but temperatures will still
be several degrees above normal with some areas possibly still
near High HeatRisk. Although ensemble spread increases through the
middle of next week, the model cluster analysis (about 2/3 of
solutions) favors slightly lower heights and some modest relief
from the heat. The NBM temperature guidance reflects this scenario
calling for temperatures to gradually lower through the end of
next week, but still remaining slightly above normal and probably
at or above 100 degrees. Moisture levels next week will remain
very low with almost no chance of rain over the lower deserts. A
few spurious ensemble members somewhat increase moisture levels by
the end of next week, with perhaps a low end risk of a mountain
shower.
&&
.AVIATION...Updated at 0455Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns anticipated. High pressure across
New Mexico will result in a drying trend along with light winds
and mostly clear skies. Anticyclonic flow around the high will
also promote an earlier switch to westerly flow, generally in the
early afternoon Saturday.
Southeast California/Southwest Arizona including KIPL and KBLH:
After a period of breezy westerly flow behind an outflow
boundary, southerly winds have returned to the Imperial Valley.
The southerly component to the flow will continue at KIPL and KBLH
through Saturday, with occasional periods of 10-15 kt winds,
particularly at KBLH. Otherwise, mostly clear skies are
anticipated.
&&
.FIRE WEATHER...
Sunday through Thursday:
Strong high pressure will persist over the region through at least
early next week providing dry conditions and above normal
temperatures. High temperatures through Tuesday are expected to
run several degrees above normal with some lower desert areas
likely reaching 110 degrees on Sunday and Monday. A gradual
cooling trend is then expected into the latter half of next week.
Min RH levels will mostly be between 10-15% through the period,
while max RHs generally range from 30-45%. Winds will remain
fairly light through the period while following typical diurnal
patterns. Some afternoon breeziness is also likely most days
starting Tuesday with gusts up to around 20 mph.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Sunday to 8 PM MST Monday for
AZZ530>544-546-548>551-553>555-559.
CA...Excessive Heat Warning from 10 AM Sunday to 8 PM PDT Monday for
CAZ561-565>567-569-570.
&&
DISCUSSION...Hodges/Kuhlman
AVIATION...Hirsch
FIRE WEATHER...KuhlmanPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
604 PM MST FRI SEP 10 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0410 PM TSTM WND GST 18 NNW COYOTE WELLS 32.99N 116.07W
09/10/2021 M42 MPH IMPERIAL CA MESONET
FISH CREEK MOUNTAINS RAWS. TIME ESTIMATED
FROM RADAR.
&&
INSThe national radar mosaic for the moment the first event began.
24 excessive heat, 3 heat. Local standard time, as filed.
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.
Four direct fatalities were 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.
A couple from Rhode Island started hiking around noon on the 12th at Brown's Ranch Trailhead in Scottsdale. After splitting up during the hike, the wife never returned to their meeting location. Local authorities from various agencies responded to search for the missing woman. Shortly after 2100MST, local authorities found the missing woman who had succumbed to the heat.
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, North Phoenix/Glendale | 2021-09-11 | Unknown | Direct | ||
| Heat, Southeast Valley/Queen Creek | 2021-09-11 | Unknown | Direct | ||
| Heat, Buckeye/Avondale | 2021-09-11 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2021-09-12 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2021-09-14 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2021-09-14 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2021-09-14 | Unknown | Direct | ||
| Excessive Heat, Northwest Valley | 2021-09-12 | Unknown | Direct | ||
| Excessive Heat, Gila Bend | 2021-09-13 | Unknown | Direct | ||
| Excessive Heat, Cave Creek/New River | 2021-09-12 | 57 | Female | Outside/Open Areas | 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: 1077616, 1077617, 1077618, 1077620, 1077622, 1077624, 1077703, 1077704, 1077706, 1077708, 1077709, 1077710, 1077711, 1077712, 1077713, 1077715, 1077716, 1077717, 1077718, 1077719, 1077720, 1077721, 1077722, 1077725, 1077726, 1077755, 1077679.