How to Stay Safe During an Extreme Heat Warning

Quick Answer

An extreme heat warning, as renamed by the National Weather Service in March 2025, signals dangerously high temperatures that pose a significant health risk. To stay safe, immediately reduce outdoor activities, move to air-conditioned spaces, drink plenty of water, and check on vulnerable individuals such as elderly neighbors or those with chronic health conditions.

These warnings indicate conditions where heat-related illnesses like heat stroke and heat exhaustion are likely without proper precautions.

Key Facts

The National Weather Service renamed "Excessive Heat Warnings" to "Extreme Heat Warnings" in March 2025 as part of a hazard simplification project
An Extreme Heat Warning means extremely dangerous heat conditions are occurring or imminent
During such warnings, temperatures can exceed 100 degrees Fahrenheit in many regions, with Phoenix metro areas seeing 110-112 degrees
Heat warnings have been extended in states like Oregon and Arizona in recent years due to sustained dangerous temperatures
Overnight temperatures also remain dangerously high during these events, limiting natural cooling
Millions of people globally are impacted by extreme heat, with climate change contributing to more frequent and intense events
Cooling centers are often opened in affected areas to provide relief for those without air conditioning
Health risks include heat stroke, heat exhaustion, and worsening of pre-existing conditions

Background and Context

Extreme heat warnings are not new weather phenomena, but their naming and communication have evolved significantly. Prior to March 2025, the National Weather Service used the term "Excessive Heat Warning" to describe the most severe heat events.

The change to "Extreme Heat Warning" was part of the Hazard Simplification project, an effort to make alert names clearer and more intuitive for the public. The logic was straightforward: "Extreme" is a more universally understood term than "Excessive" when describing life-threatening conditions.

The first Extreme Heat Warnings under the new system were issued during the summer of 2025, affecting regions from the Pacific Northwest to the Southwest and the Mid-Atlantic. For example, Oregon saw an extreme heat warning extended into August 12, 2025, with temperatures threatening 100 degrees.

In Arizona, Phoenix metro areas faced temperatures between 110 and 112 degrees, prompting First Alert Weather Days. Philadelphia and surrounding areas experienced an extreme heat warning with feels-like temperatures pushing 100 degrees.

These events are not isolated. Extreme heat impacts millions of people worldwide, and the frequency of such warnings is increasing.

The National Weather Service's HeatRisk tool, which provides category definitions for heat hazards, was also updated alongside the naming changes. This system helps communicate not just the temperature but the level of risk, with Extreme Heat Warning corresponding to the highest risk level (100% HeatRisk description).

Understanding this context is crucial because heat is the deadliest weather-related hazard in the United States, often surpassing floods, hurricanes, and tornadoes in annual fatalities. The importance of these warnings extends beyond comfort.

When an extreme heat warning is in effect, the dangers are real and immediate. Heat stroke can occur within minutes of exposure to extreme temperatures, and the risk is compounded by high humidity, which reduces the body's ability to cool itself through sweating.

Urban areas are particularly vulnerable due to the heat island effect, where concrete and asphalt absorb and re-radiate heat, making nighttime temperatures remain dangerously high.

Detailed Explanation

What Triggers an Extreme Heat Warning

The National Weather Service issues an Extreme Heat Warning based on a combination of factors, not just a single temperature threshold. The criteria vary by region because populations acclimate to different climates.

For example, a temperature of 100 degrees in Phoenix may not trigger a warning if it's typical for that area, but the same temperature in Portland, Oregon, would be more likely to warrant an alert. The key factors include:

Actual temperature: How hot the air temperature is expected to reach
Heat index: The "feels-like" temperature that combines heat and humidity
Duration: How long the heat is expected to last, especially if overnight temperatures do not drop significantly
Overnight lows: If temperatures remain above 80 degrees at night, the body gets no relief, increasing risk
Public health impact: Historical data on heat-related illnesses in the area

In practice, an Extreme Heat Warning typically means temperatures are forecast to reach 100 degrees or higher for two or more consecutive days, or when the heat index reaches dangerous levels. The updated HeatRisk system now provides a clearer five-level scale, with Extreme Heat Warning corresponding to the highest level where heat-related illnesses are expected.

How to Prepare Before a Warning Is Issued

Preparation begins long before the warning appears on your phone. The most critical step is ensuring your home can provide a cool refuge.

If you have air conditioning, have it serviced before summer. If you do not have air conditioning, identify cooling centers in your area.

Many communities open public buildings such as libraries, community centers, or designated cooling stations during extreme heat events. Other preparation steps include:

Stock up on supplies: Keep extra water, electrolyte drinks, and non-perishable food that doesn't require cooking
Check medications: Some medications can affect heat sensitivity or dehydration risk. Consult your doctor if you take diuretics, antihistamines, or blood pressure medications
Prepare your home: Install window reflectors or blackout curtains to block sunlight. Use fans strategically—box fans in windows can draw in cool air at night
Know your neighbors: Identify elderly or isolated individuals who might need help. Check on them regularly
Have a plan for pets: Animals are also vulnerable to heat. Ensure they have shade and water, and never leave them in a parked car

What to Do During an Extreme Heat Warning

When an Extreme Heat Warning is in effect, your priority is to minimize heat exposure and stay hydrated. The National Weather Service's guidance is clear: avoid outdoor activities, stay hydrated, and seek air-conditioned environments.

Here is a step-by-step approach:

1. Limit outdoor activity: If you must go outside, do so during the early morning or evening when temperatures are slightly lower.

Avoid strenuous activity altogether. If you work outdoors, take frequent breaks in the shade or air conditioning.

The body's cooling mechanisms are overwhelmed in extreme heat, and even short periods of exertion can lead to heat exhaustion or heat stroke. 2.
Hydrate constantly: Drink water every 15-20 minutes, even if you do not feel thirsty. Thirst is a late indicator of dehydration.

Avoid alcohol, caffeine, and sugary drinks, which can worsen dehydration. Electrolyte drinks can help replace salts lost through sweating, but water should be your primary fluid.

3. Find air conditioning: Spend time in air-conditioned spaces.

If your home is not air-conditioned, go to a cooling center, shopping mall, library, or public building. Even a few hours in air conditioning can reduce your risk of heat-related illness.

Fans can help, but when temperatures are above 95 degrees, fans may actually increase heat stress by blowing hot air onto your body. 4.
Cool your body: Take cool showers or baths. Apply cold compresses to your neck, wrists, and ankles.

Wear lightweight, light-colored, loose-fitting clothing. A wide-brimmed hat can provide shade if you must be outside.

5. Check on others: Monitor elderly family members, neighbors with health conditions, and anyone who lives alone.

Children and pregnant women are also more vulnerable. Pets should be kept indoors with access to water, and never left in cars—even with windows cracked, temperatures inside a car can rise rapidly to lethal levels.

Recognizing and Responding to Heat-Related Illnesses

Knowing the signs of heat exhaustion and heat stroke can save lives. Heat exhaustion is less severe but can progress to heat stroke if untreated.

Heat exhaustion symptoms:

Heavy sweating
Weakness or fatigue
Dizziness or fainting
Nausea or vomiting
Cool, moist skin
Headache

What to do: Move to a cool place, loosen clothing, sip water, and apply cool cloths. If symptoms worsen or last more than an hour, seek medical attention.

Heat stroke symptoms:

High body temperature (103 degrees or higher)
Hot, red, dry, or damp skin
Rapid, strong pulse
Confusion or loss of consciousness
Throbbing headache
Nausea

What to do: Heat stroke is a medical emergency. Call 911 immediately.

While waiting for help, move the person to a cooler place, and try to lower body temperature with cool cloths or a cool bath. Do not give fluids if the person is unconscious or confused.

Common Questions and Misconceptions

1. "I can just use a fan to stay cool." Fans are helpful at lower temperatures, but when the air temperature exceeds 95 degrees, fans can actually increase heat stress by blowing hot air onto your body.

They do not cool the air; they only move it. In extreme heat, fans should be used only if you can also access air conditioning or a cool shower.

The safest approach is to move to an air-conditioned environment. 2.
"I don't need to worry because I'm healthy and young." While age and health status increase risk, extreme heat can affect anyone. Heat stroke can strike healthy young adults who overexert themselves or underestimate the heat.

The body's cooling mechanisms have limits, and when temperatures reach dangerous levels, even athletes and outdoor workers are at risk. No one is immune to the effects of extreme heat.

3. "Drinking coffee or beer is fine because they're liquids." Alcohol and caffeine are diuretics, meaning they increase fluid loss from the body.

Drinking beer or coffee during an extreme heat warning can worsen dehydration. Water is the best choice, followed by electrolyte drinks that replace salts lost through sweating.

Sports drinks can be useful, but be aware of their sugar content, which can cause stomach discomfort in some people. 4.
"The warning is only about daytime heat." Overnight temperatures matter just as much. When temperatures do not drop below 80 degrees at night, the body gets no chance to recover from daytime heat exposure.

This is why prolonged heat waves are particularly dangerous—the cumulative stress builds over days. In Oregon and Arizona, warnings were extended in 2025 precisely because overnight temperatures remained dangerously high.

5. "If it's cloudy, the heat isn't dangerous." Cloud cover does not eliminate the danger.

Humidity can make the heat index higher than the actual temperature, and ultraviolet radiation can still cause sunburn through clouds. The combination of high humidity and high temperatures is especially dangerous because it prevents sweat from evaporating, which is the body's primary cooling mechanism.

Always check the heat index, not just the temperature.

What to Watch For

As extreme heat events become more frequent, understanding how to respond to warnings is increasingly important. Here are practical steps to stay ahead of the danger:

Monitor local weather alerts: Sign up for weather alerts from the National Weather Service or local news outlets. The new Extreme Heat Warning naming is designed to be clearer, but you should also understand the difference between a Heat Advisory (less severe) and an Extreme Heat Warning (most severe).

Heat.gov provides a live map of current alerts. 2.
Know your local cooling resources: Before heat strikes, find out where cooling centers are located in your area. Many cities publish these locations online or through 311 information lines.

Libraries, community centers, and senior centers often serve as cooling sites. Have a plan for how to get there if you do not have transportation.

3. Prepare your home: Consider investing in window reflectors, blackout curtains, or reflective window film to reduce indoor temperatures.

If you have air conditioning, ensure it is serviced. If you rely on window units, clean the filters regularly.

For those without air conditioning, identify a friend or relative with AC who can host you during the worst heat. 4.
Check your medications: Some medications can increase heat sensitivity or affect the body's ability to regulate temperature. Talk to your doctor about whether your prescriptions or over-the-counter medications could pose risks during extreme heat.

Antihistamines, blood pressure medications, and some psychiatric drugs are common culprits. 5.
Plan for power outages: Extreme heat often strains the power grid. Have a backup plan for cooling if the electricity goes out.

Battery-powered fans, a cooler with ice packs, and a list of nearby cooling centers can help. If you rely on medical devices that require power, have a backup battery or generator.

6. Look out for vulnerable populations: Elderly individuals, young children, pregnant women, and those with chronic illnesses are most at risk.

Make it a habit to check on neighbors and family members during heat warnings. If you are caring for someone who is bedridden or has limited mobility, ensure they have access to water and cooling.

7. Recognize the signs of heat illness: Learn the symptoms of heat exhaustion and heat stroke.

Early intervention is key. If you or someone else shows signs of heat exhaustion, act quickly.

Do not wait until symptoms become severe.

Frequently Asked Questions

What is the difference between a Heat Advisory and an Extreme Heat Warning?

A Heat Advisory is issued when heat conditions are expected to be uncomfortable but not immediately life-threatening, typically when the heat index is expected to reach 100-105 degrees for a short period. An Extreme Heat Warning, the most severe alert, is issued when extremely dangerous heat is occurring or imminent, with conditions likely to cause heat-related illnesses.

The National Weather Service updated these categories in March 2025 to use clearer language, replacing "Excessive Heat Warning" with "Extreme Heat Warning."

How long does an Extreme Heat Warning typically last?

The duration varies by event. In Philadelphia in June 2025, an Extreme Heat Warning lasted from Sunday morning to Wednesday evening—about three days.

In Oregon in August 2025, a warning was extended by an extra day because temperatures remained dangerous. Warnings can last anywhere from 24 hours to several days, depending on the weather pattern.

The National Weather Service provides start and end times for each alert.

Can I exercise outdoors during an Extreme Heat Warning?

No. The National Weather Service explicitly advises avoiding outdoor activities during an Extreme Heat Warning.

Strenuous exercise in extreme heat can quickly lead to heat exhaustion or heat stroke, even in healthy individuals. If you must exercise, do so early in the morning or late in the evening when temperatures are lower, keep sessions short, and stay well-hydrated.

Better yet, move workouts indoors to an air-conditioned space.

Are pets at risk during an Extreme Heat Warning?

Yes, pets are vulnerable to heat stroke and dehydration. Never leave pets in a parked car, even with windows cracked—temperatures inside can rise to lethal levels within minutes.

Pets should be kept indoors during the hottest parts of the day. Ensure they have access to fresh, cool water at all times.

Signs of heat stroke in animals include excessive panting, drooling, weakness, vomiting, and collapse. If you suspect your pet is overheating, move them to a cool area, offer water, and contact a veterinarian.

What should I do if I don't have air conditioning?

If you do not have air conditioning, seek out air-conditioned public spaces such as libraries, shopping malls, community centers, or designated cooling centers. Many cities open cooling centers during extreme heat warnings.

You can also take cool showers or baths, use damp cloths on your skin, and spend time in the lowest level of your home (basements are naturally cooler). Avoid using the oven or stove, which can heat up your living space.

If possible, stay with a friend or relative who has air conditioning.

Reference Notes

Information in this article is based on publicly available sources. Some details may change over time.

Verify with official sources before acting.

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