Watch, advisory, warning
The National Weather Service issues heat products on a rising scale, and the words carry specific meanings that are worth learning once. A watch is issued when dangerous heat is possible in the next few days but not certain. It is a planning signal: move the outdoor work earlier, check the air conditioning, find out where the nearest cooling center is before you need it. An advisory or a warning means the heat is occurring or is imminent, with a warning reserved for the more dangerous end. At that point you are not preparing, you are responding.
| Product | What it means | What you do |
|---|---|---|
| Watch | Dangerous heat is possible, usually a day or several out | Reschedule outdoor work, test the AC, locate a cooling center |
| Advisory | Heat that is uncomfortable and risky for vulnerable people is occurring or imminent | Limit exertion in the afternoon, check on neighbors |
| Warning | Heat dangerous to the general population is occurring or imminent | Stay out of the sun during the hottest hours, get to cooled space |
The exact temperature or heat index that triggers each one is not a single national number. It is set by the local NWS office and reflects what that population is acclimated to, which is why the same reading can produce a warning in Seattle and nothing at all in Phoenix. Do not memorize a number. Sign up for alerts, and note that Wireless Emergency Alerts to your phone are reserved for the most severe events, so routine heat products will not always buzz.
Heat exhaustion and heat stroke are different emergencies
This is the distinction that matters most, because one is treated on the spot and the other is a 911 call. The dividing line is not how hot the person feels. It is mental status.
| Heat exhaustion | Heat stroke | |
|---|---|---|
| Mental state | Awake, oriented, complaining | Confused, slurring, combative or unconscious |
| Skin | Pale, cool, heavily sweating | Hot; may be dry, may still be sweating |
| Other signs | Nausea, headache, weakness, cramps | Very high body temperature, rapid pulse |
| What to do | Move to shade or AC, loosen clothing, sip cool fluids, rest | Call 911, then cool aggressively while you wait |
| Watch for | No improvement in about half an hour means seek care | Never give fluids to someone who is not fully alert |
Heat stroke is a medical emergency in the same category as a stroke or a heart attack. If someone working in the sun stops making sense, that is the sign, not the thermometer.
What actually cools someone down
Get them out of the sun and into shade or air conditioning. Take off extra clothing. Then get water on the skin and air moving over it, because evaporation is what removes heat fastest. A garden hose, a wet sheet and a box fan, or a tub of cool water all work. Cold packs at the neck, the armpits and the groin help because large blood vessels run close to the surface there. Do not stop cooling because they seem a little better, and do not wait for the ambulance before you start.
Alcohol and heavy caffeine work against you by pushing fluid out, and drinking only when thirsty is already behind. If you are sweating through a shirt an hour, plain water alone will eventually leave you short on salt. Our sweat rate and hydration calculator puts a number on what a given work rate costs you, and the daily water intake calculator is the baseline before you add any of that.
Working through a hot week
The dangerous window is the middle of the afternoon, roughly noon to five, and heat lags the sun so the hottest hour is usually well after solar noon. If the work can move to early morning, move it. If it cannot, the three things that keep crews upright are water, shade and rest, taken on a schedule rather than when someone feels bad, because by the time a person feels bad they are already behind. Rotate the heaviest tasks. Pair people up so someone notices the confusion before the person having it does.
Acclimatization is real and it is slow. Somebody returning from vacation, or a new hire in their first week, is at meaningfully higher risk than the same person a fortnight later doing identical work. Build up gradually.
Cooling centers and who is most at risk
In most of the United States, emergency management is a county function, sometimes a city one. That is who opens cooling centers, and the list lives on the county or city website or comes through a 211 call rather than through a national agency. Libraries, senior centers, community centers and malls are common sites. Find out where yours are before a heat wave, because the day you need one is the day the website is slow.
Risk concentrates in specific places: people over sixty-five living alone, infants, anyone with heart or kidney disease, people on diuretics or certain psychiatric medications, outdoor workers, and anyone without working air conditioning. A daily phone call to an older relative during a heat wave is a genuinely effective intervention. If a home has no AC, a fan alone stops helping once the indoor air is hotter than skin — at that point the fan is moving hot air across a person and a few hours somewhere cooled is the better answer. Running the AC harder for a week shows up on the bill, and the appliance power calculator will tell you roughly how much.
Cars, children and pets
A closed car in summer sun climbs far past the outside temperature within minutes, and cracking a window changes it very little. Small children lose heat control faster than adults do, and a car is the single most common way heat kills children in this country. There is no version of "just for a minute" that is safe.
The habit that works is a physical one: put something you cannot leave without — a phone, a bag, a work badge — on the back seat next to the car seat, so opening the back door is part of arriving. If you see a child alone in a parked car and they appear distressed, call 911 immediately. The same applies to dogs, who cannot sweat and cool almost entirely by panting.
Questions people ask
Is a heat warning worse than a heat watch?
Yes. A watch means dangerous heat is possible and you have time to prepare. A warning means it is happening or is about to happen. People routinely have these backwards, which is worth fixing once: watch is a forecast of possibility, warning is a statement about now. The specific temperatures behind each are set by your local National Weather Service office and vary by region, so check weather.gov for your area rather than relying on a remembered number.
How do I tell heat exhaustion from heat stroke?
Look at mental status, not at the skin or the thermometer. Someone with heat exhaustion is awake and oriented, usually pale and sweating heavily, and they get better in shade with rest and fluids. Someone with heat stroke is confused, slurring, behaving strangely or unconscious, and their skin is hot. That is a 911 call. Start cooling them with water and moving air while you wait, and do not try to give fluids to anyone who is not fully alert.
Does a fan help during extreme heat?
Up to a point. A fan cools by helping sweat evaporate, so it works well while the air is cooler than skin. Once indoor air is hotter than body temperature, a fan is moving hot air over a person and does much less, and for a frail or older person it can give a false sense that the room is safe. If the house cannot be cooled, spending the hottest hours somewhere air conditioned is the reliable answer.
Where do I find a cooling center?
Emergency management in most of the US is run at the county level, occasionally the city, so the list of open cooling centers comes from your county or city government rather than a national source. Check their website or social media, or call 211, which connects to local health and human services in most areas. Libraries, senior centers and community centers are common locations. Look this up before a heat wave rather than during one.