Strong high pressure with abundant sunshine and dry air allowed for temperatures to reach excessive heat warning criteria for periods of time May 6-9. According to the Maricopa County Department of Public Health, there were three heat-associated fatalities in Maricopa County during this period.
Every event with a place to put it; 2 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 with abundant sunshine and dry air allowed for temperatures to reach excessive heat warning criteria for periods of time May 6-9. According to the Maricopa County Department of Public Health, there were three heat-associated fatalities in Maricopa County during this period. As reported to Phoenix, the data are aggregrated and represent monthly values for several combined communities. Unfortunately, specifics such as age, gender, location of fatality, and circumstances cannot be obtained.
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 May 5, 9:12 PM MST, 2 hours 48 minutes earlier.
Area Forecast Discussion
National Weather Service Phoenix AZ
912 PM MST Sat May 5 2018
.UPDATE...Updated Aviation Discussion.
&&
.SYNOPSIS...
High pressure will intensify over the region through the weekend
resulting in extremely hot weather. Record high temperatures are
very likely Sunday with lower elevation readings topping out in
the 104 to 108 degree range. This will lead to an excessive heat
risk for many areas. Typical late spring heat will persist
throughout next week with most communities still reaching 100
degrees.
&&
.DISCUSSION...
A strong ridge of high pressure has become established over the
desert SW this afternoon warming our temperatures into the triple
digits as 500 mb heights have reached 585 dm in the latest 12Z
soundings. Surface high pressure over the Great Basin and Texas
has created easterly flow over south central Arizona this
morning/afternoon aiding to the warming via adiabatic
compression. Clear skies exist overhead as the atmosphere remains
void of any substantial moisture with PW values sitting around a
quarter of an inch. Elsewhere, a trough of low pressure is moving
into Northern California and the Pacific Northwest bringing light
showers and clouds to the area.
Models are in excellent agreement of building this ridge into
Sunday with 500 mb heights approaching 590 dm and 850 mb
temperatures shooting north of 26 C. Values of this magnitude are
at the 99th percentile of climatology and as one could expect,
will bring unseasonably warm conditions and possibly record
breaking heat across the area. Our latest forecast calls for 106 F
at Sky Harbor come Sunday which would be a record high for the
date. One caveat is that high clouds from the aforementioned
Pacific Northwest trough will move over our area tomorrow and
possibly inhibit warming by a degree or two. Nevertheless, very
warm temperatures will continue into Sunday.
By Monday, a weak shortwave moving through the Great Basin will
act to partially weaken the ridge. This will act to dampen our
temperatures for Monday, however only by a degree or two.
Regardless, temperatures should be below warning threshold for all
areas by Monday. Tuesday through Thursday, the ridge will only
modestly weaken with high temperatures staying nearly stationary
for the workweek. Conditions will continue to stay bone dry with
mostly sunny skies prevailing through the period with no chance of
rain.
During the latter half of next week and into the weekend,
stronger energy moving from the Pacific NW through the northern
and central Rockies will, at the very least, flatten ridging over
the forecast area and dampen heights and thicknesses. However,
operational and ensemble output late in the week has suddenly
become extremely dispersive with respect to the pattern evolution
resulting from this northern stream wave. The 00Z operational
ECMWF continues its trend of deepening a trough over the four
corners while previous GFS runs slide this energy downstream into
the Upper Midwest. NAEFS members have almost every type of
solution in between, but in general more CMC members, along with
the latest GFS are beginning to agree with the ECMWF. Given the
uncertainty, could only trend the forecast towards an ensemble
mean resulting in a slightly warmer than normal forecast.
&&
.AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL:
Winds are forecast to remain mostly light tonight while trending to
the east by midnight. By mid morning breezy easterly winds will
develop with gusts near 16kt through early afternoon. After that
light winds will resume and follow typical diurnal headings.
Skies will be partly cloudy with SCT-BKN high clouds through
Sunday morning and increasing high clouds by mid afternoon through
Sunday night.
Southeast California/Southwest Arizona including KIPL and KBLH:
With no aviation concerns expect light to light and variable winds
with occasional moderate winds near 8-12kt favoring typical diurnal
shifts. Skies will be partly cloudy with SCT-BKN high clouds through
Sunday morning and increasing high clouds by mid afternoon through
Sunday night.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Tuesday through Saturday:
Warm and dry conditions will persist Tuesday through Friday with
high temperatures 10+ degrees above normal. Afternoon minimum
humidity will fall into the single digits every afternoon with
overnight recoveries ranging between 20 and 30 percent for most
areas. Typical afternoon May winds will prevail with speeds
between 10 and 20 mph along with the usual upslope gustiness.
Cooler and possibly breezier conditions may exist on Saturday
although there is large uncertainty between models.
&&
.CLIMATE...
Record high temperatures for Sunday:
Date Phoenix Yuma
---- ------- ----
May 6 105 in 1947 107 in 1963
&&
.SPOTTER INFORMATION STATEMENT...
Spotter activation will not be needed.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM to 8 PM MST Sunday for AZZ530-
532-533-536-539-540-543-544-546-548-550-551-553-559.
CA...Excessive Heat Warning from 10 AM to 8 PM PDT Sunday for
CAZ565>567-569-570.
&&
DISCUSSION...Wilson/MO
AVIATION...Sawtelle
FIRE WEATHER...Wilson
CLIMATE...MOThe national radar mosaic for the moment the first event began.
2 excessive heat. Local standard time, as filed.
Phoenix airport reached 106 degrees on May 7, resulting in excessive heat warning conditions. According to the Maricopa County Department of Public Health, there were 2 heat fatalities (1 direct and 1 indirect).
Phoenix airport reached 106 degrees on May 9th, resulting in excessive heat warning conditions. According to the Maricopa County Department of Public Health, there was 1 indirect heat fatality.
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, East Valley | 2018-05-06 | Unknown | Direct | ||
| Excessive Heat, East Valley | 2018-05-07 | Unknown | Indirect | ||
| Excessive Heat, Cave Creek/New River | 2018-05-09 | Unknown | Indirect |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, May 2018
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: 854799, 854804.