ACC News Brief
Environmental Health U.S. Southwest
Forecast and active warning — not an event-attribution finding
Southwest heat warnings forecast dangerous temperatures through the weekend
What happened
On August 26, the National Weather Service forecast daytime highs of 110–115°F in the hottest Southwest locations through the end of the week. For Yavapai County below 4,000 feet, including the Verde Valley, NWS Flagstaff expected 105–110°F and kept an Extreme Heat Warning in effect from 10 a.m. August 26 through 8 p.m. August 28 MST. Other active Phoenix-office warnings extended through August 29 and listed afternoon temperatures as high as 117–118°F in some lower-desert areas. These are forecasts and alerts that can be updated, not final observed temperatures or an attribution study.
ACC context
The immediate public-health instruction comes from the weather warning itself. The Fifth National Climate Assessment finds that extreme heat is already harming Southwest residents and is expected to increase with climate change, but this particular alert does not quantify how much human-caused warming changed this event.
Why it matters
NWS warned that most people in the verified Yavapai warning area could face heat-related illness without effective cooling or hydration, especially during prolonged outdoor exposure. Outdoor workers, older adults, people with health conditions, people without reliable cooling, and unhoused residents can face disproportionate risk.
What to watch
- Updated NWS warning boundaries, extensions, cancellations, and point forecasts; use the live NWS alert rather than treating this snapshot as permanent advice.
- Overnight lows and HeatRisk, because limited nighttime relief can compound health stress.
- Local cooling locations, public-health guidance, and eventual observed temperatures compared with the forecast.
Sources & evidence
- National Weather Service point forecast for Cottonwood, ArizonaNOAA National Weather Service point forecast updated August 26, 2026 at 11:32 a.m. MST, valid through September 1. It confirms the active warning, point location, local forecast office, and update period.
- NWS Flagstaff Extreme Heat Warning for Yavapai County below 4,000 feetOfficial alert issued August 26, 2026 at 6:03 a.m. MST. VTEC /O.CON.KFGZ.XH.W.0014.260826T1700Z-260829T0300Z/; it forecasts about 105–110°F below 4,000 feet and remains a forecast that can be updated.
- National Extreme Heat Warning summaryLive NOAA/NWS warning summary checked August 26, 2026. It confirms multiple Southwest warning areas with differing forecast temperatures and end times; the page changes as alerts are updated.
- Fifth National Climate Assessment, Chapter 28: SouthwestU.S. Global Change Research Program regional assessment published in 2023. It supports the broader finding that extreme heat is already harming Southwest residents and is expected to increase, but it does not attribute this individual warning event.
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