Excessive Heat and Heat in Arizona, September 8 to 13, 2018

Name: Excessive Heat and Heat in Arizona, September 8 to 13, 2018
Start: 2018-09-08T10:00
End: 2018-09-13T20:00
Location: Arizona

September 8 to 13, 2018 · NWS PSR · 8 events in 6 counties and zones

High pressure over the region led to dangerous heat between September 8th through the 13th. Five direct heat fatalities were reported by the Maricopa County Department of Public Health.

Where it happened

Every event with a place to put it; 8 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 5
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 8

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.

What happened

The episode as NWS PSR wrote it up.

High pressure over the region led to dangerous heat between September 8th through the 13th. Five direct heat fatalities were reported by the Maricopa County Department of Public Health.

What forecasters said that day

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 8, 4:45 AM MST, 5 hours 15 minutes earlier.

Area forecast discussion, Sep 8, 4:45 AM MST, 5 hours 15 minutes before

Area Forecast Discussion
National Weather Service Phoenix AZ
445 AM MST Sat Sep 8 2018

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Strong high pressure over the region will continue to provide
overall dry and warm conditions through much of next week.
The warmest day will be today as high temperatures reach above
110 degrees across the deserts of southwest Arizona and southeast
California while readings top out around 105 degrees in the
Phoenix area. Slightly cooler readings, but still above seasonal
normals are forecast for next week.

&&

.DISCUSSION...
A warm and dry second week of September is in store for the
Desert Southwest with temperatures running on average 3 to 6
degrees above normals. A strong Pacific high off the southern
California coast continues to bring weak northerly flow across the
region and 500mb heights above 90% of climatology across southeast
California and southwest Arizona. The warmest day still looks to
be today as 850mb temperatures peak at around 29C resulting in
highs reaching above 110 degrees across the western deserts and
generally 105-107 degrees across the south-central Arizona
deserts. Excessive Heat Warnings are in effect for today across
portions of southeast California and southwest Arizona.

The Pacific high will begin to weaken tonight while a Gulf surge
also brings increased boundary layer moisture to much of southern
Arizona and the Lower Colorado River Valley starting Sunday
morning. These factors will knock off a couple degrees for Sunday,
but highs will still top out around 110 degrees across the
western deserts. Based on Sunday's forecast highs, heat risk
drops enough to not warrant extending the Excessive Heat Warning
for another day.

The high pressure center shifts eastward early next week
eventually parking itself over northern Mexico and southern New
Mexico. Heights aloft over the Desert Southwest really don't
change much throughout the week and temperatures will be fairly
stable. Forecast highs for next week fall between 103-107 degrees
across the lower deserts.

Further drying today should keep any isolated afternoon showers
and thunderstorms confined mainly over the White Mountains.
Moisture levels will remain a problem through the upcoming week
while warm air aloft and weak lapse rates also hinder convection.
Steering flow Sunday through at least Thursday should be out of
the southwest, so any showers or weak storms that do develop along
the Rim or in the White Mountains will not be able to drift
toward our CWA. Models have overall shown a drying trend with the
past couple model runs, so it is doubtful southern Arizona will
see much if any storm activity next week.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL, and
Southeast California/Southwest Arizona including KIPL and KBLH:

There are minimal aviation weather concerns through today as winds
will remain fairly light, outside of a few afternoon gusts, and
follow typical diurnal tendencies. Otherwise, mostly clear skies
will prevail.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday:
Temperatures will remain around 5 degrees above normal through
most of the week. A gradual increase in moisture will result in a
return to at least slight chances of thunderstorms by the middle
of the week. Minimum RH will rise into the 20-30 percent range
during this period across the deserts of south-central Arizona.
Winds should generally remain light and diurnally driven.

&&

.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 AZZ530-532-536.

CA...Excessive Heat Warning from 10 AM this morning to 8 PM PDT this
     evening for CAZ561-566-567-569-570.

&&

DISCUSSION...Kuhlman
AVIATION...Deemer
FIRE WEATHER...Rogers

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

5 heat, 3 excessive heat. Local standard time, as filed.

Excessive Heat, Yuma

When: September 8, 10:00 AM MST to 8:00 PM MST
Where: Yuma forecast zone
Reported by: County Official
Coordinates: 32.769, -113.906 (the zone’s center; the record gives no point)

Excessive Heat, Gila River Valley

When: September 8, 10:00 AM MST to 8:00 PM MST
Where: Gila River Valley forecast zone
Reported by: County Official
Coordinates: 32.769, -113.906 (the zone’s center; the record gives no point)