Strong high pressure over the region allowed for temperatures to climb above 110 degrees on the 9th and 10th, promoting excessive heat conditions. According to the Maricopa County Department of Public Health, 5 heat-associated fatalities occurred during this event.
Every event with a place to put it; 13 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 over the region allowed for temperatures to climb above 110 degrees on the 9th and 10th, promoting excessive heat conditions. According to the Maricopa County Department of Public Health, 5 heat-associated fatalities occurred during this event.
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 9, 4:47 AM MST, 5 hours 13 minutes earlier.
Area Forecast Discussion
National Weather Service Phoenix AZ
447 AM MST Sun Aug 9 2020
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
Above normal temperatures and abnormally dry conditions are
expected through the coming week. Daily highs across the lower
deserts will mainly top out at around 110 degrees through Tuesday
before likely warming to between 112 and 114 degrees during the
latter part of the week. The dry conditions will at least allow
overnight lows to be near seasonal normals.
&&
.DISCUSSION...
Current water vapor imagery continues to show an unusually dry
atmosphere across southern California and Arizona with PWATs in
the bottom 10% of climo for this time of year. Surface dew points
are reflective of this dryness with widespread readings in the
30s and 40s, more typical of May and June. The nearly stationary
weak trough just off the California coast and the subtropical
ridge centered over the Southern Plains will keep the Desert
Southwest under this dry southwesterly flow into the middle part
of the week. Very little will change over the next several days,
but highs should tick upward another degree or two today, likely
hitting 112 in the Phoenix area to 110 degrees across the western
deserts. What little moisture is still available across the
eastern Arizona high terrain should produce a few isolated showers
and weak storms this afternoon east of Globe.
The Excessive Heat Warning for the Phoenix area and portions of
Gila County is in effect for today and Monday. NBM guidance has
recently lowered temperatures 1-2 degrees for Monday, but will
keep the warning going into Monday as a matter of consistency. Low
level flow on Monday will turn more westerly across eastern
Arizona, leading to further drying of the boundary layer and
essentially ending any rain chances for Arizona.
Starting Tuesday, the subtropical ridge to our east will begin
expanding westward with the center of the ridge shifting closer to
southwest New Mexico. Despite the ridge moving closer to Arizona,
heights aloft on Tuesday will remain stable as a weak shortwave
trough is forecast to move through southern Utah and far northern
Arizona. NBM temperature guidance still shows Tuesday as being the
"coolest" day of the week even though highs are still shown to
top out between 109-110 degrees. We should also see some modest
increase in surface dew points (closer to 50-55 degrees) starting
Monday night into Tuesday due to a more favorable low level flow
off the Gulf of California. Unfortunately, this slight increase in
low level moisture will not bring back any rain chances due to
the moisture being quite shallow and a strong capping inversion
seen aloft.
For the latter half of the week, the bulk of ensemble guidance is
now pointing toward the center of the high pressure ridge shifting
northwestward into Arizona by Thursday. Additionally, the ridge is
also forecast to strengthen Thursday through Saturday with 500mb
heights potentially reaching near 596dm. There is still some
decent model spread with the position and strength of the ridge,
but the overall trend points toward another heat episode starting
either Wednesday or Thursday. Forecast highs by Wednesday notch
upward a few degrees to between 110-112 degrees. Starting Thursday
and extending through next weekend, median NBM guidance indicates
highs may range from 112-114 degrees, or close to record
temperatures. The position of the high center will likely
determine how long this next heat wave will last and for now the
center looks to remain over Arizona into next weekend. Very
limited moisture levels through Friday should keep the entire
area dry, but as the high center is shown drifting farther to the
northwest, we may be able to finally see some high terrain storm
chances by next weekend.
&&
.AVIATION...Updated at 1146Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns through the next 24 hours. Winds will remain
light, aob 10 kts, favoring typical diurnal tendencies.
Variability is possible through the morning and early-afternoon.
Isolated gusts to 18 kts are possible in the afternoon. Skies
should remain mostly clear aside from a few fair weather cumulus
in the afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns for at least the next 24 hours. Winds remain
light and variable through mid-afternoon at KIPL before westerly
sundowner winds kick in. KBLH will see winds increase to around 10
kts in the afternoon out of the south to southwest with gusts up
to 18 kts. Skies will remain clear.
&&
.FIRE WEATHER...
Tuesday through Saturday:
Most days will be hot and dry. Minimum humidity values will drop
below 15% for almost everywhere while overnight recoveries will
mostly top out in a 20-30% range. Winds will generally follow
typical diurnal/terrain influences at light and some typical
afternoon breezes. Thunderstorm activity will be very limited, and
non existent through at least the first half of the week.
Increasing moisture by Friday/Saturday looks better which may be
enough for isolated thunderstorms to form over the higher terrain
north and east of Phoenix.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 9 AM this morning to 8 PM MST Monday
for AZZ537-540-542>544-546-548-550-551-556-560-562.
CA...None.
&&
DISCUSSION...Kuhlman
AVIATION...Benedict
FIRE WEATHER...AD/KuhlmanThe national radar mosaic for the moment the first event began.
12 excessive heat, 1 heat. Local standard time, as filed.
Four heat-associated fatalities were reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances and location unavailable.
One heat-associated fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender, circumstances and 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 | 2020-08-09 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2020-08-09 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2020-08-10 | Unknown | Direct | ||
| Excessive Heat, Central Phoenix | 2020-08-10 | Unknown | Direct | ||
| Heat, Central Phoenix | 2020-08-11 | Unknown | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2020Every state in 2020This day in weather historyWarnings in Arizona, August 2020
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: 992710, 992936, 992937, 992938, 992939, 992940, 992941, 992942, 992943, 992944, 992945, 992946, 992711.