A late-season heat wave settled over a wide stretch of the country this week, and the National Weather Service kept Extreme Heat Warnings running from the Arizona and Nevada deserts to parts of the southern Plains. The alerts cover two different kinds of danger at once: dry desert heat pushing past 110 degrees in California and Nevada, and a muggier, humidity-driven heat index climbing above 110 across Arkansas and Oklahoma. Forecasters describe the exposure as measured in days rather than hours, since the warnings span consecutive afternoons with little overnight cooling.
Why Death Valley and the Colorado River Valley Are Forecast to 116 Degrees
The Extreme Heat Warning issued by the National Weather Service office in Las Vegas covers portions of northwest Arizona, southeast California and southern Nevada, an area that includes Death Valley National Park, Lake Havasu, Lake Mead and Lake Mohave on both the Arizona and Nevada sides, the Las Vegas Valley, the Moapa and Pahrump valleys, and the upper Colorado River Valley. Forecasters projected high temperatures of 112 to 116 degrees in Death Valley and the Colorado River Valley, with 105 to 110 expected across the Las Vegas, Moapa and Pahrump valleys. The warning ran from 10 a.m. to 8 p.m. local time on September 10, one in a string of daily reissued warnings that has covered the region since September 8.
Neighboring forecast offices posted similar numbers for the rest of the desert Southwest: afternoon highs of 106 to 112 degrees were expected across Imperial County and the Imperial Valley, where the warning extends latest, into Friday evening, while the Phoenix metro area was forecast to reach 105 to 109 and the Yuma area 107 to 110.
A Muggier, Humidity-Driven Heat Wave Across the Southern Plains
Farther east, a different mechanism is at work. The National Weather Service office in Tulsa issued heat warnings for parts of northwest and west central Arkansas and eastern Oklahoma, including Tulsa, Muskogee and Sebastian County, with heat index values forecast above 110 degrees. Parts of southern Texas registered projected heat index readings in a similar range. Heat index blends air temperature and humidity to estimate how hot conditions feel to the body, and added moisture interferes with the evaporative cooling that sweat normally provides. That is why a location far from any desert can carry the same warning label as Death Valley even with a lower thermometer reading.
What Separates a Heat Warning From an Advisory
An Extreme Heat Warning means dangerous heat is happening or about to happen and residents should take action immediately, while a Heat Advisory covers conditions that are dangerous but fall short of warning criteria. Local forecast offices set their own thresholds based on what a region’s population is acclimated to, which is why a heat index that would draw only an advisory in Phoenix in July can meet warning criteria in Arkansas in September. Heat Advisories this week reached beyond the warned areas, covering additional parts of Arkansas and Oklahoma along with California’s San Joaquin Valley and nearby mountain communities.
The Health Toll Behind the Alert Language
Federal data illustrates why the Weather Service treats heat as its own category of emergency. A Centers for Disease Control and Prevention fact sheet estimates that in an average year, heat-related illness accounts for 67,512 emergency department visits, 9,235 hospitalizations and 702 deaths across the United States. CDC surveillance of hospital visit data has found that the federal region covering Arkansas, Louisiana, New Mexico, Oklahoma and Texas records the highest rate of heat-related emergency visits in the country, a pattern that lines up with this week’s Plains warnings.
Who Faces the Greatest Risk This Week
Older adults, infants and young children, pregnant people, and those with heart, lung or kidney disease face the greatest danger of severe outcomes during an extended heat event. Some medications, including certain diuretics, antipsychotics and drugs with anticholinergic effects, can blunt the body’s ability to sweat or regulate fluid balance, raising risk further. Outdoor workers in construction, agriculture and delivery carry a distinct occupational hazard during peak afternoon hours; the warning text itself repeats guidance from the Occupational Safety and Health Administration recommending frequent rest breaks in shaded or air-conditioned locations.
Basic Precautions as the Warnings Run Into the Weekend
The Weather Service’s instructions are blunt: drink fluids before feeling thirsty, stay in air conditioning when possible, limit strenuous activity to early morning or evening, and check on relatives and neighbors at least once during a multi-day event. Vehicle interiors reach lethal temperatures within minutes, so no child or pet should be left inside a parked car even briefly. Anyone showing confusion, a fast and strong pulse, or hot and dry skin should be treated as a medical emergency and moved to a cool location while help is called. Because these warnings are reissued daily rather than posted once for the whole event, residents in the affected counties are advised to check the current alert for their area rather than rely on earlier forecasts. Most metro areas inside the warned zones operate cooling centers during declared heat events, typically at libraries, community centers and senior centers, and local emergency management offices or 211 lines can point residents to the nearest one.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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