Weather watch, warning or advisory: what each alert means for your health

This page is not a live alert or forecast. It explains alert types and cannot tell you what is in effect where you are. For current alerts, go to weather.gov and enter your city or ZIP code, or listen to NOAA Weather Radio.

The short answer

• Watch: get ready. Conditions favor a hazard, but whether it happens, where, or when is still uncertain.
• Warning: act now. The hazard is happening, about to happen, or very likely, and it threatens life or property.
• Advisory: be aware and take care. The hazard is less serious than a warning but can turn dangerous without caution. A heat or cold advisory still describes dangerous conditions, especially for people at higher risk (see below).
• The heat names changed in 2025. On or about March 4, 2025, the National Weather Service (NWS) renamed the Excessive Heat Watch and Warning to the Extreme Heat Watch and Extreme Heat Warning. The Heat Advisory kept its name.
• Your phone will not warn you about everything. The NWS does not send its heat or air-quality alerts as phone emergency alerts. Check those yourself.

The three words, side by side

The NWS is the official source of U.S. warnings for life-threatening weather. Each local office sets its own trigger points, because heat or snow that is dangerous in one place may be routine in another.

You may also see an outlook, which flags a hazard that might develop further ahead. A watch can later become a warning or an advisory, or be canceled.

Alert names you may see now

The NWS has been simplifying alert names. Some apps and older guides still use the old names.

• Cold, on or about October 1, 2024: Wind Chill Watch and Warning became the Extreme Cold Watch and Extreme Cold Warning, and Wind Chill Advisory became the Cold Weather Advisory, to make clear that cold can be dangerous with or without wind. Hard Freeze alerts were folded into Freeze alerts.
• Heat, on or about March 4, 2025: Excessive Heat became Extreme Heat for watches and warnings, which the NWS said better conveys that heat is dangerous.

Heat alerts

The Centers for Disease Control and Prevention (CDC) names these higher-risk groups for heat: adults 65 and older, infants and young children, people with chronic medical conditions, pregnant people, outdoor workers, athletes, and people without air conditioning. Some medicines also make heat harder on the body; see medicines that can raise your risk in a heat wave.

Extreme Heat Watch (get ready). Plan to stop major outdoor activities if a warning follows. Without air conditioning, find the nearest cooling center now or arrange to stay with someone who has it. Refill prescriptions and set up daily check-ins.

Heat Advisory (act, especially if you are at higher risk). The NWS describes it as dangerous heat below warning level and labels it "Take Action." Postpone outdoor activity in the hottest hours if you can. Outside, drink water and take frequent shade breaks. Stay somewhere cool in the afternoon and evening.

Extreme Heat Warning (act now). Avoid outdoor activity, especially in the heat of the day. Stay in air conditioning as much as possible, including overnight. Check on family and neighbors.

For every heat alert:

• Fans: CDC advises using a fan only when the indoor temperature is below 90°F. Above that, find air conditioning.
• Cooling centers: CDC suggests calling 2-1-1 or your local health department. Hours can change during a heat wave, so call ahead.
• Cars: Never leave a child, a person with a disability, or a pet in a parked car. The NWS warns a car can get dangerously hot even on a mild day in the 70s, and a cracked window barely helps.
• Fluids: Drink water even if you are not thirsty. If a clinician has limited your fluids, or you have fluid build-up, ask them before drinking more. Do not take salt tablets unless a clinician told you to.
• Work: California's workplace heat rules follow the temperature at work, not NWS alerts; see California's two workplace heat standards.

For the full range of heat illness and how to prevent it, read Heat-Related Illness: Protecting Yourself in the Central Valley.

HeatRisk and, in California, CalHeatScore

The NWS also publishes HeatRisk, an experimental 0 (green) to 4 (magenta) scale for the next seven days. It weighs how unusual the heat is for the season, how long it lasts (including warm nights), and CDC health data. It adds to official alerts but does not replace them. CDC's guidance, in brief:

In California, the state's Office of Environmental Health Hazard Assessment runs CalHeatScore, launched at the end of 2024. It ranks upcoming heat from 0 (low) to 4 (severe) by ZIP code, is updated daily, and its map can show county cooling centers. If an alert and a color scale seem to disagree, follow the more protective advice, especially if you are at higher risk.

Cold and freeze alerts

An Extreme Cold Warning means dangerously cold air or wind chill is expected or happening. A Cold Weather Advisory covers dangerous cold below warning level. Freeze Warnings and Frost Advisories are issued in the growing season with crops in mind, but they also signal nights near or below freezing for anyone without reliable heat.

CDC lists these people as more likely to develop hypothermia (a dangerous drop in body temperature): older adults without enough food, clothing or heat; babies sleeping in cold bedrooms; people outdoors for long periods, including people without housing; and people who drink alcohol or use drugs. Hypothermia can happen above 40°F in someone chilled by rain, sweat or cold water.

Heating and outages: Never use a generator, grill, camp stove, or other gasoline, propane or charcoal device inside a home, garage or carport. Run a generator outdoors, at least 20 feet from doors, windows and vents. Do not heat your home with a gas oven. Put battery-powered carbon monoxide (CO) alarms, or alarms with battery backup, outside sleeping areas and on every floor.

Smoke and air-quality alerts

The NWS issues an Air Quality Alert to pass along an air pollution alert from an air quality agency, such as a state environmental agency. A Dense Smoke Advisory means smoke has cut visibility to a quarter mile or less.

These alerts point to the Air Quality Index (AQI). At 101 to 150 (orange), sensitive groups, including people with heart or lung disease, older adults, children and teens, should cut back on heavy outdoor exertion. At 151 to 200 (red), everyone should cut back on prolonged or heavy exertion, and sensitive groups should avoid it. CDC adds pregnant people and people with diabetes or chronic kidney disease to those at higher risk from wildfire smoke.

When smoke is coming, CDC suggests a "clean room" you can close off from outside air, with a portable air cleaner, and a NIOSH Approved respirator, such as an N95, if you must go out. See what the Air Quality Index numbers mean and, for the Valley, Air Quality and Respiratory Health in Fresno and the Central Valley.

Fire weather alerts

A Fire Weather Watch means critical fire weather is possible but not yet happening. A Red Flag Warning means critical fire weather, such as strong wind with very dry air and dry vegetation, is happening or expected soon. The NWS advises extreme care with open flames.

These alerts are about fire risk, not smoke. Keep a bag ready with your medicines and medicine list, and know more than one way out of your area. In California, utilities may also cut power to high-risk areas during dangerous fire weather so their lines do not start a fire. State regulators call these Public Safety Power Shutoffs a "measure of last resort." If anyone at home depends on powered medical equipment, see a power outage plan for a household that uses medical equipment.

Flood alerts

A Flood Watch means flooding is possible. A Flood Warning means flooding is about to happen or already is. A Flash Flood Warning means a sudden, violent flood is about to happen or already is: if you are in a flood-prone area, get to higher ground immediately. Flash floods can reach places where it is not raining. A Flood Advisory means flooding below warning level that can still become dangerous.

• Never walk or drive into floodwater. The NWS says 6 inches of moving water can knock an adult down, and about 12 inches can carry away most cars. The water can hide washed-out roads, power lines, chemicals and sharp objects.
• Stay out of any room where water covers outlets or cords. If moving water traps you, go to the highest point you can reach and call 911.
• If you use a wheelchair, oxygen or other equipment, or need help leaving home, arrange your ride and destination when the watch is issued, not when the warning comes.

How alerts reach you, and where they fall short

• Wireless Emergency Alerts (WEA) arrive on compatible phones with a special tone and vibration. They are free and need no sign-up. The NWS sends them for a short list of urgent warnings, such as tornado, major flash flood, destructive thunderstorm, hurricane, dust storm and tsunami warnings, not for heat, cold or air quality. Local officials can also send them for evacuations. Phones set to Spanish can show Spanish alerts when the agency sends them.
• Local alert sign-ups from your county or city can send texts, calls or emails with more detail. In California, the state Office of Emergency Services links to every county's sign-up at CalAlerts.org.
• NOAA Weather Radio broadcasts NWS warnings, watches and forecasts 24 hours a day. A battery-powered weather radio helps when power or phone service is unreliable.
• weather.gov shows every alert for your location. Full NWS alerts usually spell out WHAT, WHERE and WHEN, plus instructions.

Always check when an alert was issued and when it expires. An app summary or a saved screenshot can be out of date, so read the full alert when a decision depends on it.

Before alert season: a checklist for higher-risk households

• Turn on emergency alerts in your phone's settings, and sign up for your county's alerts.
• Save weather.gov for your ZIP code, and learn where to find HeatRisk (and CalHeatScore in California).
• Pick two cool places you can reach, such as a cooling center, a library or a friend's home with air conditioning, and how you will get there.
• Ask your clinician or pharmacist whether any of your medicines raise heat risk, and whether your fluid limit changes in hot weather.
• If you use powered medical equipment or medicine that must stay cold, make an outage plan.
• Choose a daily check-in partner for heat and cold alerts, and test CO alarms monthly.
• Keep a ready bag: medicine list, the extra medicine your pharmacy or plan allows, chargers and copies of key cards. Before fire season, get a portable air cleaner and well-fitting respirators.

Sources

1. Local and California Severe Weather Products: Watches, Warnings, and Advisories — National Weather Service, San Joaquin Valley/Hanford, CA office, accessed October 21, 2026.
2. Weather glossary: Watch; Advisory; Outlook; Extreme Heat Warning; Heat Advisory; Cold Weather Advisory; Dense Smoke Advisory — National Weather Service, accessed October 21, 2026.
3. Service Change Notice 24-88: Renaming of Excessive Heat Watch and Warning to Extreme Heat Watch and Warning — National Weather Service Headquarters, September 5, 2024.
4. Hazard Simplification: How are NWS Heat Products Changing? — National Weather Service fact sheet, accessed October 21, 2026.
5. Service Change Notice 23-44 Updated: Consolidated NWS Public Weather Program Products Related to Cold — National Weather Service Headquarters, March 26, 2024.
6. National Weather Service revises watch, warning and advisory products for cold — National Weather Service, accessed October 21, 2026.
7. Watch/Warning/Advisory map: list of products and colors — National Weather Service, accessed October 21, 2026.
8. Understanding Heat Alerts — National Weather Service, accessed October 21, 2026.
9. During a Heat Wave and Children, Pets and Vehicles — National Weather Service, accessed October 21, 2026.
10. Heat-related illness — National Weather Service, accessed October 21, 2026.
11. Heat and Your Health: Risk Factors — CDC, last reviewed June 25, 2024.
12. About Heat and Your Health — CDC, last reviewed July 20, 2026.
13. How to Use the HeatRisk Tool and Air Quality Index — CDC, last reviewed September 18, 2025.
14. NWS HeatRisk (experimental) — National Weather Service, accessed October 21, 2026.
15. CalHeatScore and CalHeatScore Methods Documentation, Version 2.0 — California Office of Environmental Health Hazard Assessment, January 2026.
16. Preventing Hypothermia — CDC, last reviewed August 25, 2026.
17. Avoiding Carbon Monoxide Poisoning — CDC, last reviewed August 26, 2026; and About Carbon Monoxide Poisoning — CDC, last reviewed January 12, 2026.
18. What to Know About Generators and Carbon Monoxide — U.S. Consumer Product Safety Commission, 2022.
19. NWS to issue Air Quality Alerts — National Weather Service, Denver/Boulder, CO office; and Air Quality — National Weather Service, Austin/San Antonio, TX office; accessed October 21, 2026.
20. AQI Basics and Be Smoke Ready — AirNow, U.S. Environmental Protection Agency, accessed October 21, 2026; and Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI) — U.S. Environmental Protection Agency, EPA-403/B-26-003, May 2026.
21. Wildfire smoke: who is at higher risk and Preparing for Wildfires — CDC, last reviewed August 24, 2026.
22. Understanding Wildfire Warnings, Watches and Behavior — National Weather Service, accessed October 21, 2026.
23. Public Safety Power Shutoffs — California Public Utilities Commission, accessed October 21, 2026.
24. Flood Warning vs. Watch, During a Flood and Turn Around Don't Drown® — National Weather Service, accessed October 21, 2026.
25. Wireless Emergency Alerts — National Weather Service, accessed October 21, 2026.
26. How To Sign Up For Alerts In Your County — California Governor's Office of Emergency Services, accessed October 21, 2026.
27. NOAA Weather Radio All Hazards — National Weather Service, accessed October 21, 2026.
28. California Code of Regulations, Title 8, Section 3395: Heat Illness Prevention in Outdoor Places of Employment — California Department of Industrial Relations, accessed October 21, 2026.