US Heat Wave Puts More Than 100 Million People Under Alerts as Dangerous Temperatures Spread

 US Heat Wave Puts More Than 100 Million People Under Alerts as Dangerous Temperatures Spread

More than 100 million people across the United States were placed under some form of heat alert as a powerful heat wave spread from the West through the Great Plains, Midwest and South.

The dangerous weather brought triple-digit temperatures to several major cities, while high humidity pushed heat index values into potentially life-threatening territory. Some regions were also facing severe thunderstorms, damaging winds and possible flooding along the northern edge of the heat dome.

At least 40 million people were under extreme heat warnings by Monday, July 27, 2026, according to the Associated Press.

At a Glance

What is happening?

A broad area of high atmospheric pressure is trapping hot air over large parts of the United States, creating several days of extreme heat.

How many people are affected?

More than 100 million Americans were under some form of heat alert on Sunday, July 26. At least 40 million people were under extreme heat warnings by Monday.

Where is the worst heat?

The most dangerous conditions extend from parts of California and Nevada through the Great Plains, Midwest, Mississippi Valley and South.

How hot could it get?

Temperatures in several cities were forecast to exceed 100 degrees Fahrenheit. Heat index values of 105 to 115 degrees were possible across parts of the central United States, while some desert communities could approach 120 degrees.

When will temperatures improve?

A cold front may bring temporary relief to parts of the Upper Midwest, but dangerous heat is expected to continue longer across the central, southern and southwestern United States.

Why Are More Than 100 Million Americans Under Heat Alerts?

The large number reflects the enormous geographic reach of the heat wave.

Heat advisories and extreme heat warnings covered communities stretching from Southern California through the Plains and into the Midwest and South. The affected area includes major metropolitan regions as well as rural communities.

The National Weather Service issues different heat alerts depending on the expected severity of conditions and the climate of a particular region.

A heat advisory generally means hot temperatures and humidity could cause heat-related illnesses.

An extreme heat warning indicates a more serious and potentially life-threatening situation in which heat-related illnesses are expected to increase significantly.

The exact thresholds are not identical everywhere because people, buildings and public infrastructure in different regions have varying levels of heat tolerance.

Which Parts of the United States Are Experiencing the Worst Heat?

The most intense conditions have affected the central and southern United States, along with parts of the Southwest.

Cities expected to reach triple-digit temperatures included Phoenix, Las Vegas, Rapid City, Omaha, Denver, Dallas and Kansas City.

Rapid City, South Dakota, reached 112 degrees on Saturday, setting a daily record. Las Vegas was forecast to reach approximately 112 degrees, while Phoenix was expected to climb to around 109 degrees.

Palm Springs, California, was forecast to experience temperatures near 112 degrees during the week, with conditions potentially approaching 120 degrees by the following weekend.

From Texas to the Upper Midwest, humidity made the heat feel even worse. Heat index values between 105 and 115 degrees were expected across a broad area.

Why Does the Heat Feel Hotter Than the Actual Temperature?

Humidity prevents sweat from evaporating efficiently.

The human body normally cools itself when perspiration evaporates from the skin. When the surrounding air contains a large amount of moisture, sweat evaporates more slowly and the body has greater difficulty releasing heat.

The heat index combines the air temperature and humidity to estimate how hot the conditions feel to the human body.

For example, the actual air temperature may be below 100 degrees, but high humidity can make it feel like 110 degrees or more.

Warm nighttime temperatures also increase the danger.

Temperatures were expected to remain near 90 degrees overnight in Phoenix and Las Vegas, while cities such as Dallas, Kansas City and Omaha could experience lows near 80 degrees.

When nighttime temperatures remain high, homes and human bodies have less opportunity to cool down. This can increase the risk of heat-related illness, especially for people without reliable air conditioning.

What Is Causing the US Heat Wave?

The extreme weather is being driven by a strong area of high pressure commonly called a heat dome.

A heat dome forms when atmospheric conditions trap a large mass of hot air over a region. The high-pressure system suppresses clouds and limits the movement of cooler weather systems.

As the trapped air sinks toward the ground, it can become even hotter.

This pattern may persist for several days, producing intense daytime temperatures and unusually warm nights across a wide area.

The current heat dome stretches from the Southwest and southern Plains through parts of the Midwest.

Which Cities Could Reach Triple-Digit Temperatures?

At least seven major cities were expected to reach or exceed 100 degrees during the heat wave.

Forecast temperatures included:

Las Vegas: approximately 112 degrees

Phoenix: approximately 109 degrees

Rapid City: approximately 105 degrees

Denver: approximately 102 degrees

Omaha: above 100 degrees

Dallas: above 100 degrees

Kansas City: above 100 degrees

Denver’s expected high of 102 degrees would exceed the city’s July 26 record of 100 degrees, which was set in 1910.

Exact temperatures may change as forecasts are updated. Residents should monitor their local National Weather Service office for the most accurate information.

Are Severe Storms Also Expected?

Yes. Severe thunderstorms are possible across parts of the Upper Midwest, Great Lakes and Ohio Valley.

The northern edge of the heat dome can create an unstable environment where extreme warmth and humidity provide energy for powerful thunderstorms.

Possible hazards include:

Damaging wind gusts

Large hail

Frequent lightning

Localized flash flooding

Isolated tornadoes

Parts of Nebraska and southeastern South Dakota could experience thunderstorm wind gusts between 60 and 80 miles per hour.

The severe-weather threat was expected to shift toward the Great Lakes and Ohio Valley on Monday.

This creates a difficult combination of hazards. Communities experiencing extreme heat may also face power outages caused by severe storms, removing access to air conditioning when it is needed most.

Who Is Most at Risk During Extreme Heat?

Extreme heat can affect anyone, but some people face a much greater risk of serious illness.

Those most vulnerable include:

Older adults

Infants and young children

Pregnant people

People with heart, lung or kidney conditions

People taking medications that affect hydration or body temperature

Outdoor workers

Athletes

People without air conditioning

People experiencing homelessness

People living alone

Pets and animals left outdoors

Older adults may not recognize thirst as quickly, while young children heat up faster than adults.

People with chronic health conditions may also have greater difficulty regulating their body temperature.

What Are the Signs of Heat Exhaustion?

Heat exhaustion occurs when the body loses too much water and salt through sweating.

Common symptoms include:

Heavy sweating

Weakness or fatigue

Dizziness

Headache

Nausea or vomiting

Muscle cramps

Cool or clammy skin

A fast or weak pulse

A person showing signs of heat exhaustion should be moved to a cool or air-conditioned location.

Loosen unnecessary clothing and apply cool, wet cloths to the skin. Provide water if the person is fully conscious and able to drink safely.

Seek medical help if symptoms worsen or do not improve.

What Are the Warning Signs of Heat Stroke?

Heat stroke is a medical emergency.

Possible symptoms include:

Confusion

Disorientation

Loss of consciousness

Seizures

Very high body temperature

Hot or flushed skin

A strong or rapid pulse

Anyone suspected of having heat stroke requires immediate emergency medical assistance.

Move the person to a cooler area and begin cooling them with wet cloths, ice packs or cool water while waiting for emergency responders.

Do not leave the person alone.

How Can People Stay Safe During the Heat Wave?

People in affected areas should spend as much time as possible in air-conditioned buildings, especially during the hottest hours of the afternoon.

Recommended precautions include:

Drink water regularly, even before feeling thirsty.

Avoid alcohol and excessive caffeine, which may contribute to dehydration.

Limit strenuous outdoor activity.

Move exercise and outdoor work to the early morning when possible.

Wear lightweight, loose-fitting and light-colored clothing.

Use cooling centers if air conditioning is not available at home.

Check on elderly relatives, neighbors and people who live alone.

Never leave children or pets inside parked vehicles.

Keep pets indoors or provide shade and plenty of fresh water.

Check local weather alerts before traveling or attending outdoor events.

People working outside should take frequent breaks in shaded or air-conditioned areas.

What Has Been Confirmed?

More than 100 million Americans were under some form of heat alert on Sunday, July 26, 2026.

At least 40 million people were under extreme heat warnings by Monday, July 27.

Triple-digit temperatures affected or threatened several major cities.

Heat index values between 105 and 115 degrees were expected across parts of the central United States.

Some desert areas could experience temperatures approaching 120 degrees.

Severe thunderstorms, damaging winds, large hail and possible flooding were also expected in parts of the Midwest and Great Lakes.

What Remains Uncertain?

The total number of people under alerts will change as the National Weather Service issues, extends or cancels warnings.

The timing of meaningful relief will vary by region.

The exact locations of the strongest thunderstorms cannot be predicted far in advance.

Some temperature records will not be officially confirmed until weather observations have been reviewed.

Explainedly Analysis

The scale of this heat wave shows why the air temperature alone does not fully describe the danger.

A forecast high of 98 degrees may sound less alarming than a temperature above 100 degrees. However, when high humidity pushes the heat index to 110 degrees and nighttime temperatures remain elevated, the health risk can become more serious.

The combination of heat and severe weather creates an additional threat.

Strong storms can damage power lines and cause outages, leaving homes without air conditioning while dangerous heat remains in place.

That means preparation should begin before the hottest part of the day.

Charging phones, identifying nearby cooling centers, storing drinking water and checking on vulnerable relatives or neighbors can make a meaningful difference.

The most useful response is not panic. It is early action based on official local forecasts and heat warnings.

Key Takeaways

More than 100 million Americans were under heat-related alerts as the heat wave spread across the country.

At least 40 million people were under extreme heat warnings by Monday.

The Midwest, South, Great Plains and Southwest were among the most affected regions.

Heat index values could reach between 105 and 115 degrees in some locations.

Desert communities could approach 120 degrees.

Severe thunderstorms and possible flooding may affect some areas experiencing extreme heat.

Residents should monitor local National Weather Service alerts, stay hydrated and use air-conditioned spaces whenever possible.

Frequently Asked Questions

Is the entire United States experiencing the heat wave?

No. The most dangerous heat is concentrated across the West, Great Plains, Midwest and South, although the affected areas may change as the weather system moves.

What is the difference between a heat advisory and an extreme heat warning?

A heat advisory means hot conditions could cause heat-related illness. An extreme heat warning indicates a more dangerous situation in which serious heat-related illnesses are more likely.

Can digital thermometers accurately measure outdoor heat?

Household thermometers may show different readings depending on where they are placed. Official temperatures are measured using standardized equipment positioned away from direct sunlight and heat-reflecting surfaces.

Should people avoid going outside completely?

Not necessarily, but prolonged or strenuous activity should be avoided during the hottest hours. Outdoor activities should be moved to the morning or evening whenever possible.

Can fans prevent heat stroke?

Fans may help when temperatures are moderately hot, but they may not be enough during extreme heat. Air conditioning, cooling centers, cool showers and wet cloths provide more effective cooling.

Sources:

National Weather Service

Associated Press

ABC News

National Weather Service regional forecast offices