Long-duration extreme heat risk: what the outlook means and how to prepare

What changed

CPC sees a broad, persistent heat signal into early September

The Climate Prediction Center’s August 21 assessment favors a long-duration extreme-heat event across a large part of the southern and central United States. CPC posts a high risk for much of the Desert Southwest, Southern Rockies, Southern and Central Plains, and Lower Mississippi Valley on August 29–30. A moderate risk covers a larger surrounding area through September 1, while a slight risk extends across still more of the southern and central U.S. through September 4.

CPC also identifies a rapid-onset-drought risk in parts of the Central and Southern Plains and the Middle and Lower Mississippi Valley. That is a separate climate hazard: it describes the risk that unusually hot, dry conditions could quickly deplete surface moisture. It is not a declaration that every highlighted county is already in drought.

The Weather Prediction Center’s August 22 extended discussion supports hazardous heat continuing across the Southern Plains and Lower Mississippi Valley during the nearer forecast period. These national products provide useful context, but your local NWS forecast remains the place to check expected highs, nighttime lows, humidity, timing, and active alerts.

Read the label before acting

An outlook, forecast, watch, advisory, and warning are not interchangeable

A national risk area can be useful days in advance, but it does not tell you the exact temperature at your home or workplace. Read the product name, issue time, valid period, affected area, and instructions before deciding what to do.

CPC hazards outlook

A probability-based early signal covering a broad region and multi-day period. Use it to review plans and watch for later forecast changes. It is not a local alert.

Local NWS forecast

The expected temperature, humidity, overnight conditions, and timing for a specific place. Forecast details become more useful as the date gets closer, but a forecast is not itself a watch or warning.

Extreme Heat Watch

Conditions are favorable for an extreme-heat event, but the occurrence or timing remains uncertain. Be prepared and know where you can stay cool if a warning follows.

Heat Advisory

Dangerous heat is expected or occurring, but conditions are not expected to reach warning criteria. Take action to reduce exposure and strenuous activity.

Extreme Heat Warning

Extremely dangerous heat is expected or occurring. Take action, stay in an air-conditioned place as much as possible, and follow the warning instructions.

More than the afternoon high

Humidity, warm nights, duration, and personal exposure shape the risk

Air temperature is only one part of heat stress. The NWS heat index combines temperature and relative humidity to estimate how hot conditions feel. NWS HeatRisk adds information about the unusualness and duration of the heat, and it is supplementary to official watches, warnings, and advisories—not a replacement for them.

• Check hourly conditions, not only the daily high.
• Look at nighttime temperatures because limited overnight cooling can increase strain during a multi-day event.
• Consider how long you will be outside, the intensity of the activity, shade, airflow, humidity, and access to cooling.
• Do not use one national map or one heat-index value as a substitute for your local forecast and health needs.
• Never leave a child, disabled adult, older adult, or pet in a parked vehicle.

Prepare before the hottest days

Make the cooling plan while there is still time to adjust

A Week‑2 outlook gives households, caregivers, employers, and event organizers time to reduce exposure before local alerts are issued. The plan should work even if the heat lasts several days or a power problem affects normal cooling.

1. Check that cooling equipment works and identify an air-conditioned place you can reach safely.
2. Move strenuous outdoor work, exercise, travel loading, and yard work away from the hottest part of the day when possible.
3. Arrange frequent shade or cooling breaks and make drinking water readily available.
4. Check on older adults, people with disabilities, pregnant people, young children, outdoor workers, and neighbors who live alone.
5. Keep medicines as directed and ask a healthcare professional about heat if a condition or prescription affects temperature control or fluid balance.
6. Know how to receive Wireless Emergency Alerts and local NWS updates if the outlook becomes a watch, advisory, or warning.

Recognize heat illness

Heat exhaustion needs cooling; heat stroke is a 911 emergency

Heat illness can worsen quickly. Heavy sweating, weakness, dizziness, headache, nausea, muscle cramps, or fainting can signal heat exhaustion. Move the person to a cooler place, loosen clothing, apply cool wet cloths, and offer sips of water if the person is alert and able to drink. Get medical help if symptoms worsen, vomiting occurs, or symptoms last longer than an hour.

Confusion, loss of consciousness, a very high body temperature, or hot red skin—dry or damp—can signal heat stroke. Call 911 immediately, move the person to a cooler place, and cool with wet cloths or a cool bath while help is coming. Do not give the person anything to drink.

Recheck as the period approaches

The broad signal can persist while local details change

Revisit the CPC outlook for regional changes, then switch your attention to the local forecast as August 29 approaches. A city near the edge of a national risk area may have different timing or severity than a city in its center. Clouds, humidity, wind, elevation, and overnight cooling can also change the local impact.

• Check your exact location rather than the nearest large city.
• Read the full alert text, including start and end times.
• Follow local cooling-center, school, workplace, event, and public-safety instructions.
• Do not treat the absence of a warning today as proof that the later outlook will not affect you.
• Do not treat a national outlook as permission to ignore a nearer-term local warning for another hazard.