What the Aug. 19-29, 2026 Desert Southwest Heat Wave Looked Like, and How It Ended

Update, Sept. 2, 2026: Every warning described in this article has since expired. As of Sept. 1-2, the National Weather Service shows no Extreme Heat Warnings or Watches active in Phoenix, Tucson or North Texas. This article is kept as a record of the Aug. 19-29, 2026 heat episode described below.

As of Sunday, August 23, 2026, dangerous heat continued across the Southwest, then in its second week. The Phoenix, Yuma and Tucson Extreme Heat Warnings were extended again and now run through 8 p.m. Saturday, August 29 — Tucson’s warning, previously set to end earlier, now matches Phoenix’s timeline. North Texas has a separate Extreme Heat Warning running through 9 p.m. Saturday, August 24. The Arkansas, Oklahoma and Las Vegas alerts described when this article first published have since expired or downgraded: Little Rock and Memphis have no active heat alert, Tulsa has only a lower-tier Heat Advisory through tonight, and the Las Vegas Extreme Heat Warning runs through tonight, August 23.

An Extreme Heat Warning is the National Weather Service’s top-tier heat alert — issued when heat index or air temperature readings are expected to reach dangerous levels for anyone without reliable cooling and water. The exact trigger varies by local NWS forecast office rather than being one fixed nationwide number; many offices use thresholds around 105°F to 110°F. (The name changed from “Excessive Heat Warning” in 2025 as part of an NWS effort to simplify its alert language; the trigger itself didn’t change.) A Watch means those conditions are possible but not yet certain. An Advisory covers heat that’s still hazardous but a step below a Warning or Watch.

Key facts

Alert type: Extreme Heat Warnings — the NWS’s top-tier heat alert — cover Phoenix, Yuma and Tucson, plus North Texas, as of Sunday, August 23, 2026.
Arizona: Extreme Heat Warning for Phoenix, Yuma County and Tucson extended through 8 p.m. Saturday, August 29; highs of 106–114°F.
Southern Nevada / Las Vegas Valley: Extreme Heat Warning through 8 p.m. tonight, August 23; highs of 103–107°F.
North Texas: a new Extreme Heat Warning covering Dallas-Fort Worth runs through 9 p.m. Saturday, August 24.
Arkansas and Oklahoma: the Aug. 19-20 warnings have expired; Tulsa has only a lower-tier Heat Advisory through tonight, and Little Rock/Memphis have no active heat alert as of August 23.
Deaths in 2026 so far: 81 confirmed in Maricopa County, Arizona, as of Aug. 18 (587 more under investigation); 41 confirmed in Clark County, Nevada, as of July 30 (5 more pending). Neither is tied to this week’s alerts.
Power grid: a DOE emergency order covering 17 states expired August 3; no new order confirmed for this week.

Where the warnings are

Arizona, southeast California and Nevada

Arizona is under an Extreme Heat Warning covering the Phoenix metro area, Tucson and Yuma County, extended again as of August 23 and now running through 8 p.m. Saturday, August 29 — Tucson, previously on a separate shorter timeline, now expires alongside Phoenix and Yuma. Across the warned area, afternoon highs are forecast from 106°F up to 114°F. Phoenix itself is expected to see highs toward the middle of that range, 109 to 113°F — the city hit 113°F on Wednesday and recorded an overnight low of 92°F, an unusually warm night for the area. This is Phoenix’s second major heat warning stretch this summer: an earlier Extreme Heat Warning ran 18 straight days, from July 23 through August 9, before conditions eased and then returned with this week’s alert. Death Valley and the lower Colorado River corridor are forecast to reach as high as 118°F.

Southern Nevada and the Las Vegas Valley remain under an Extreme Heat Warning through tonight, August 23, at 8 p.m. Valley highs are expected to reach 103 to 107°F, with overnight lows only easing into the low-to-mid 80s — not much relief after dark.

Forecasters said Wednesday that a chance of monsoon storms moving into Arizona and southern Nevada around midweek could end the Southwest alerts early in some spots, but as of that forecast, those chances remained low — around 20% for Phoenix — and the warning window had not been shortened.

North Texas, Arkansas and Oklahoma

Farther east, North Texas — Dallas-Fort Worth and surrounding counties — is under a new Extreme Heat Warning running through 9 p.m. Saturday, August 24. The Arkansas and Oklahoma warnings described when this heat wave first hit have since expired; only Tulsa still has a lower-tier Heat Advisory in effect, through tonight, August 23.

The wider risk across the South

Beyond those warned areas, the NWS Climate Prediction Center has flagged August 19 through 21 as the highest excessive-heat-risk stretch for the broader southern Plains, Mississippi Valley and Southeast — with Texas, Oklahoma and Arkansas among the hardest hit, and neighboring states also affected — where alerts range from Heat Advisories up to Extreme Heat Warnings depending on the location. Published national estimates for how many people were under some kind of heat alert ranged from roughly 70 million to 81.2 million as of August 17-18; no single confirmed nationwide total was available for August 19 specifically. Heat index readings above 105°F, and as high as 110°F in spots including southern Georgia, coastal South Carolina, the Florida Panhandle and the Memphis area, are part of that outlook. Forecasters have said the heat across that broader region is expected to persist into at least much of the following week, even after this week’s warnings expire.

How this summer’s heat wave unfolded

This week’s heat is not an isolated event. It’s part of a broader 2026 heat wave that has moved across the country since late June — an initial heat dome settled over the eastern U.S., a second moved into the West in mid-July, and this is at least the third wave of extreme heat to hit the south-central and southwestern U.S. since then.

Late June: an initial heat dome settles over the eastern U.S., beginning this year’s heat wave.
Mid-July: a second heat dome moves into the western U.S.
July 23 – August 9: Phoenix’s earlier Extreme Heat Warning runs 18 straight days.
Late July – August 3: a DOE emergency order protects the power grid across 17 states; it has since expired.
August 16: Little Rock hits 106°F, its hottest day of 2026 so far.
August 18: Maricopa County’s confirmed 2026 heat-death toll reaches 81.
August 19 (Wednesday): Phoenix hits 113°F as this week’s Extreme Heat Warnings take hold from Arizona to North Texas; North Texas’s warning is extended into Thursday, the Phoenix/Yuma County warning is extended into Sunday, and southern Nevada is upgraded from a Watch to a full Warning.
Tonight, 8 p.m.: Extreme Heat Warnings for Arkansas and Oklahoma expire (Little Rock steps down to a Heat Advisory through Thursday evening).
Thursday, 8 p.m.: the Extreme Heat Warnings for North Texas and for the Grand Canyon below 4,000 feet expire.
Friday, 8 p.m.: the Extreme Heat Warning for Tucson/southeast California and the Extreme Heat Warning for southern Nevada expire.
Sunday, 8 p.m.: the extended Extreme Heat Warning for the Phoenix metro area and Yuma County expires.

What’s known about deaths, and what isn’t

No death or hospitalization has been confirmed as caused specifically by this week’s warnings. What is confirmed are running seasonal counts, which don’t tie to this specific week’s alerts:

Maricopa County, Arizona (home to Phoenix): 81 heat-related deaths confirmed for 2026 as of August 18, with another 587 deaths still under investigation as potentially heat-related — more than double the pace of the same point last year, when the county had confirmed 35 deaths.
Clark County, Nevada (home to Las Vegas): 41 heat-related deaths confirmed for 2026 as of July 30, with 5 more pending investigation, for 46 total. Victims’ ages ranged from 28 to 84.

Medical examiners in both counties note that heat-death investigations can take time to close, so these are running totals, not final ones. Comparable county-level death or hospitalization tallies were not found for North Texas, Arkansas or Oklahoma.

The power grid

Earlier this summer, during an earlier stretch of this same heat wave, the U.S. Department of Energy authorized an emergency order to protect the power grid across 17 states — including Arizona, Texas, Oklahoma and Arkansas — to help prevent blackouts during high demand. That order ran from late July through August 3 and has since expired. No renewed order has been confirmed for this week’s heat, and it isn’t known whether the earlier order succeeded in preventing blackouts.

Staying safe

Health officials have familiar advice for a stretch like this:

Push strenuous outdoor activity to early morning or evening.
Dress in lightweight, loose clothing.
Drink water on a regular schedule rather than waiting until you’re thirsty.
Take breaks in shade or air conditioning.
Check in on older adults, young children and anyone with a chronic illness who may be more vulnerable to heat.
Never leave a person or a pet unattended in a parked vehicle, even briefly.

Know the signs of heat exhaustion — heavy sweating, weakness, nausea — and heat stroke, which can include confusion and a body temperature above 103°F. Heat stroke is a medical emergency; officials say to call 911 if you suspect it.

Cooling centers are currently operating in Maricopa County, Arizona, and Clark County, Nevada, for residents without reliable air conditioning. No cooling-center information was available for North Texas, Arkansas or Oklahoma at publication time; residents there can check with their city or county government for local options.