What Is an Extreme Heat Warning?

An Extreme Heat Warning means a period of dangerously hot weather is happening or about to, and it is serious enough to threaten health — even for healthy people without relief from cooling and hydration. Heat is, on average, one of the deadliest forms of weather in the United States, which is why these alerts matter.

Warning vs Watch vs Advisory

• Heat Advisory — hot conditions that are uncomfortable and risky for vulnerable people. Take it seriously, but it is below the "extreme" threshold.
• Extreme Heat Watch — dangerous heat is possible in the next day or two. Make a plan to stay cool while it is easy.
• Extreme Heat Warning — that dangerous heat is now expected or underway. Act to protect yourself and others now.

If those tiers are new to you, start with watch vs warning vs advisory.

A note on the name

You may still see the older term Excessive Heat Warning. The NWS modernized its wording so the alerts read more plainly: Extreme Heat Warning and Extreme Heat Watch now carry the most serious heat messages, with Heat Advisory for lesser events. The thresholds and meaning are the same — only the labels are clearer.

Why it's about the heat index, not just the temperature

Heat alerts are triggered by the heat index — the "feels-like" temperature that blends air temperature with humidity. When humidity is high, sweat cannot evaporate to cool you, so the body struggles. That is why a 95°F afternoon can carry an Extreme Heat Warning in a humid climate but only a Heat Advisory, or nothing, in a dry one.

How to stay safe

• Get to air conditioning — your home, a friend's, a library, mall, or a public cooling center.
• Hydrate with water; skip alcohol and sugary drinks. Don't wait until you're thirsty.
• Never leave children or pets in a parked car — interior temperatures climb to deadly levels within minutes.
• Check on others — older adults, people who are ill, and anyone without air conditioning are most at risk.
• Know the warning signs of heat exhaustion and heat stroke (confusion, hot dry skin, fainting) and call for help immediately if they appear.

Check your area

See whether an Extreme Heat Warning, Watch or Advisory is active where you are with the free Weather Alerts tool. In dry, windy heat, also watch for a Red Flag Warning for fire danger.