A strong area of high pressure centered over the Great Basin migrated east over the Four Corners region, allowing for temperatures to warm up above 110 degrees on the 9th. The official high temperature in Phoenix on the 9th topped out at 111 degrees.
Every event with a place to put it; 17 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 strong area of high pressure centered over the Great Basin migrated east over the Four Corners region, allowing for temperatures to warm up above 110 degrees on the 9th. The official high temperature in Phoenix on the 9th topped out at 111 degrees. According to the Maricopa County Department of Public Health, 4 heat-associated fatalities occurred between the 9th and 10th.
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 9, 4:37 AM MST, 5 hours 23 minutes earlier.
Area Forecast Discussion
National Weather Service Phoenix AZ
437 AM MST Thu Sep 9 2021
.UPDATE...Updated Aviation Discussion.
&&
.SYNOPSIS...
Strong high pressure aloft will persist across the Southwestern U.S.
through the weekend providing above normal temperatures for much
of the region. Dry conditions will also mostly prevail, however
there will be a slight chance for afternoon isolated thunderstorms
across southeast California through Friday. After high
temperatures up to around 110 degrees for a good portion of the
lower deserts today, high temperatures through early next week
will mostly range from 105 to 109 degrees across the lower
deserts.
&&
.DISCUSSION...
Late season heat continues to be the main concern over the next
several days as the unseasonably strong upper level ridge
continues to dominate the Southwestern U.S. The center of the
ridge is now positioned more over the Four Corners area with 500mb
heights topping out around 596/597dm, at or near record climo for
the date. 500mb heights across our area have been fairly stable
the last couple days ranging from 592-594dm, or closer to 95% of
climo.
Enhanced boundary layer moisture resulting in surface dew
points mostly in the 60-65 degree range has kept recent daytime
highs from nearing daily records, but this will change today as we
anticipate stronger drying and mix out some of our surface
moisture. The drying will result in more efficient surface heating
today boosting highs several degrees over yesterday's readings.
The latest NBM shows highs today ranging from 107-110 degrees
across the south-central Arizona deserts to 108-112 degrees across
much of southwest Arizona and southeast California. These very
warm temperatures indicate areas of High HeatRisk stretching from
the Phoenix area westward through La Paz and eastern Riverside
Counties. An Excessive Heat Warning is in effect for much of the
aforementioned areas for today.
Lingering moisture across southeast California today along with
modest CAPE and lowering CIN should be enough for a few daytime
showers and thunderstorms, likely focusing more over higher
terrain areas west of the Imperial Valley. Chances across
southeast California may linger into Friday, but decreasing
moisture and lower instability should limit coverage even further
than today.
The eastward progression of the upper level ridge should push the
high center into New Mexico starting tonight while also lowering
heights slightly over southern California and much of Arizona.
With surface dew points expected to remain stable through
Saturday, the lowering heights aloft will give some slight cooling
dropping highs back to between 105-108 degrees across the lower
deserts for Friday and Saturday. Starting Sunday, the upper level
ridge is expected to begin to flatten out, but also expand
marginally higher heights back to the west over our area.
Additionally on Sunday, more dry air is expected to move into the
area pushing afternoon surface dew points down well into the 40s.
As a result, forecast highs on Sunday kick back upward to between
108-111 degrees for much of the lower deserts. Very similar
conditions are likely on Monday, but a likely incoming upper level
trough through the Northwestern U.S. may further flatten the
ridge and begin depressing heights over our region. Forecast highs
on Monday are at or maybe a degree cooler than Sunday, so it
seems very possible a good portion of the lower deserts may need
to be covered by additional Excessive Heat products for Sunday and
Monday. Upper level troughing should eventually win out across
much of the Western U.S. by the middle of next week providing a
gradual cooling trend for much of next week. Dry conditions should
continue within this pattern with a dry west southwesterly flow
very likely persisting over our region through the majority of
next week.
&&
.AVIATION...Updated at 1145Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
While there are no major aviation weather concerns in the
forecast, surface winds are not expected to follow their typical
diurnal tendencies. Easterly winds (060 to 120) are anticipated to
predominate for most, if not all, the day as the diurnal trends
fight the overall pressure gradient. There could be periods of SSE
to S winds this afternoon and early evening during peak heating
when the diurnal westerly switch would normally occur. Morning
wind speeds will generally be 4-8 kts but the afternoon speeds may
approach 10-12 kts with a few stronger gusts that could create
momentary crosswind concerns for any east/west oriented runway
configurations. Terminals located closer to mountains, such as
KIWA, KSDL, and KDVT, are better positioned to see a few hours of
an afternoon westerly wind but trends remain stronger for those
places to see wind patterns as discussed above. Otherwise,
convection in the general area should be less than it was on
Wednesday with almost zero chance for storms or associated impacts
(i.e. outflows). For tonight, a late timed gulf surge may finally
bring about a westerly shift around 06z with temporary gusts
approaching 15-20 kts. If this surge does not materialize or
reach the Valley, expect easterly winds to continue through
Thursday night/Friday morning.
Southeast California/Southwest Arizona including KIPL and KBLH:
Thunderstorm activity will be most prevalent over the Southern
California mountains and Baja spine during the early afternoon and
evening hours. Chances for storms drifting into the lower
elevations between Joshua Tree NP/Blythe/El Centro are low, at or
below 15%, so chances and confidence for any storm to occur over
either terminal is way too low to mention in the TAFs. Chances for
outflows from distant storms is also low at 25% or less.
Otherwise, southeasterly winds will predominate most of the time
at KIPL at speeds of 7-11 kts with periods of 20-25 kt gusts
possible during late evening gulf surges. At KBLH, winds will
generally vary between the SSE and SSW at 8-12 kts with occasional
gusts upwards of 20-25 kts.
&&
.FIRE WEATHER...
Saturday through Wednesday:
Strong high pressure will dominate over the Southwestern U.S.
through the weekend and likely into early next week providing dry
conditions and above normal temperatures. High temperatures are
expected to run several degrees above normal through much of the
period with some lower desert areas likely approaching 110 degrees
on Sunday and Monday. Min RH levels will range from 15-25% on
Saturday with readings dropping mostly between 10-15% starting
Sunday, while max RHs generally range from 30-50%. Winds will
overall remain light through the period while following typical
diurnal patterns.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM this morning to 8 PM MST this
evening for AZZ530-533-537-538-540>544-546-548>551.
CA...Excessive Heat Warning from 10 AM this morning to 8 PM PDT this
evening for CAZ569.
Excessive Heat Warning until 8 PM PDT this evening for CAZ561-
570.
&&
DISCUSSION...Kuhlman
AVIATION...AD
FIRE WEATHER...KuhlmanThe national radar mosaic for the moment the first event began.
14 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.
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 |
|---|---|---|---|---|---|
| Excessive Heat, Central Phoenix | 2021-09-09 | Unknown | Direct | ||
| Heat, Central Phoenix | 2021-09-10 | Unknown | Direct | ||
| Heat, East Valley | 2021-09-10 | Unknown | Direct | ||
| Heat, Gila Bend | 2021-09-10 | 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: 1077521, 1077686, 1077687, 1077688, 1077689, 1077690, 1077691, 1077692, 1077693, 1077694, 1077695, 1077696, 1077697, 1077698, 1077523, 1077524, 1077525.