US heat alerts: check your forecast, HeatRisk and local warning
Heat planning works best when you separate the forecast from the alert. Check the local forecast first, use HeatRisk to understand likely impacts, and read the full alert when your National Weather Service office issues one. Local offices set alert criteria for local conditions.
Your quick checklist
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1. Start with your local forecast
Use weather.gov to find the forecast for the place you will actually be, including the hours you expect to travel, work or exercise. A city-wide high temperature is not a complete plan for a long afternoon outdoors, a poorly cooled home or a trip across a larger forecast area.
Record the expected temperature, timing and overnight conditions, then check again before acting on a saved forecast. Conditions and local alerts can change. This guide does not replace instructions from emergency managers, employers, schools or health professionals.
2. Use HeatRisk and heat index for different questions
The NWS heat tools page explains that heat index combines air temperature and humidity, while full sun can make conditions feel hotter. It also describes HeatRisk as a color-and-number forecast that helps identify possible heat impacts over the coming seven days.
HeatRisk is planning guidance and is not the same as an official warning. NWS says it is experimental and not supported around the clock. For strenuous work or sport, the same page notes that wet bulb globe temperature uses additional factors including sun and wind. Follow the rules and guidance that apply to your activity rather than treating any one number as universal clearance.
3. Read the alert, not just its label
The NWS alert guide says local forecast offices issue heat products as conditions warrant and work with local partners on local criteria. An Extreme Heat Watch means dangerous conditions are possible but timing remains uncertain; a Heat Advisory and Extreme Heat Warning call for action at different levels of expected danger.
Open the full alert to check the affected counties or zones, start and end time, and local safety instructions. Do not transfer a threshold or alert from another city to your own area. If a warning is issued, NWS advises avoiding outdoor activity during the hottest part of the day where possible and checking on family and neighbors.
4. Make a plan that can change
Decide where you can cool down, how you will get there and who should know if your plans change. Move or shorten strenuous outdoor activity when conditions or alerts call for it. Bring water, seek shade and take breaks when outside. These are general safety actions; use local public-health and employer guidance for your situation.
If you do not have effective cooling at home, use local government or emergency-management information to find current cooling options. Confirm hours, access needs and transport before leaving. Never assume a location is open merely because it operated during an earlier heat event.
5. Treat symptoms or an emergency as urgent
A weather page cannot assess a person’s condition. If someone appears to have a medical emergency, call 911 in the United States. Move to a safer environment when possible and follow directions from emergency responders. For non-emergency health questions, seek qualified medical advice.
Check your local forecast again after an alert ends: warm nights and several hot days can keep heat stress elevated. A simple message to a neighbor, family member or colleague can identify whether they have cooling, water and a plan for the next day.
Official sources
Reviewed 2026-09-16. Open the official service for current information.
Frequently asked
- Does HeatRisk mean there is an official heat warning?
- No. HeatRisk is forecast guidance. Check your local NWS forecast and any official alert for the location, area and timing that apply to you.
- Can one heat-alert threshold apply everywhere in the US?
- No. NWS local offices issue products for local conditions. Read the alert from your own local office instead of using a threshold from another area.