☀️ Heat wave season — check before you head out
Is it too hot outside?
Real-time heat index check for any US city or ZIP code. One number, one color, clear advice — no sign-up, free forever.
What the colors mean
NOAA's heat index scale grades the feels-like temperature into five levels, from Normal to Extreme Danger.
| Feels like (°F) | Category | What can happen |
|---|---|---|
| Below 80°F | 😊 Normal | Little or no heat risk for most people. |
| 80–90°F | 🙂 Caution | Fatigue possible with prolonged exposure and physical activity. |
| 90–103°F | 😓 Extreme Caution | Heat cramps and heat exhaustion possible with prolonged exposure. |
| 103–125°F | 🥵 Danger | Heat exhaustion likely; heat stroke possible with continued exposure. |
| 125°F and above | 🚨 Extreme Danger | Heat stroke highly likely — a life-threatening emergency. |
Staying safe in extreme heat
Practical guidance for exercise, the people most at risk, pets, parked cars, and hydration — plus the symptoms that mean it's time to act.
🏃 Adjusting outdoor exercise and work
Shift your schedule
The heat index usually peaks between 3 and 6 PM — often hours after the sun is highest. Run, cycle, or do yard work before 9 AM or after sunset. On Extreme Caution days (feels like 90°F+), treat midday outdoor exercise as off-limits, not optional.
Cut intensity, not just time
In heat, your heart works 10–20 beats per minute harder at the same pace. Slow down 1–2 minutes per mile, convert hard workouts to easy ones, and give yourself 1–2 weeks to acclimatize when a heat wave arrives — fitness does not transfer instantly to hot conditions.
Build in cooling breaks
Outdoor workers should follow a work/rest cycle: at a heat index of 90–100°F, take a shaded water break at least every 30–45 minutes; above 100°F, every 15–20 minutes. Buddy up — the person overheating is often the last to notice.
Dress for evaporation
Lightweight, loose, light-colored clothing lets sweat evaporate — that evaporation is your main cooling system. Add a wide-brim hat and sunscreen: sunburned skin is measurably worse at shedding heat.
👵👶 Older adults and young children need extra care
Adults 65+
- The body's cooling response weakens with age, and thirst signals arrive late — drink on a schedule, not on thirst.
- Common medications (diuretics, beta-blockers, some antidepressants) impair heat regulation. Ask a pharmacist if a heat wave is forecast.
- Fans alone stop being protective above roughly 90°F indoors — air conditioning, a cool shower, or a cooling center is what actually lowers body temperature.
- Check on older neighbors and relatives twice a day during a heat wave. Most US heat deaths are people over 60, alone, and indoors.
Babies and young kids
- Children heat up faster than adults — smaller bodies, higher metabolic rate, less sweating capacity.
- Never cover a stroller with a blanket to shade it: it traps heat like a greenhouse. Use a clip-on parasol or a mesh cover.
- Watch for fewer wet diapers, unusual sleepiness, or a sunken soft spot — early dehydration signs in infants.
- Playground equipment (slides, rubber mats, buckles) can exceed 160°F in the sun and burn skin in seconds. Touch-test first.
🐕🚗 Pets and the hot-car trap
A parked car heats up far faster than most people expect — most of the temperature rise happens in the first 10 minutes, and cracking the windows makes almost no difference. Kids and pets should never wait in a parked car in warm weather, even "for a minute."
| Outside temp | After 10 min | After 20 min | After 30 min | After 60 min |
|---|---|---|---|---|
| 70°F | 89°F | 99°F | 104°F | 113°F |
| 80°F | 99°F | 109°F | 114°F | 123°F |
| 90°F | 109°F | 119°F | 124°F | 133°F |
| 95°F | 114°F | 124°F | 129°F | 138°F |
Approximate cabin temperatures based on published vehicle heating studies (Jan Null / San Jose State University). Actual values vary with sun, car color, and glass area.
Dogs in the heat
- Dogs cool mainly by panting — humidity hits them harder than the thermometer suggests. Heavy panting, drooling, or wobbling means stop and cool down now.
- Asphalt can be 40–60°F hotter than the air. If you can't hold the back of your hand on the pavement for 7 seconds, it's too hot for paws.
- Walk at dawn or after dusk, carry water, and remember flat-faced breeds (bulldogs, pugs) and overweight or senior dogs overheat much faster.
If you see a child or pet in a hot car
- Call 911 first — describe the car, location, and condition.
- If the child or animal appears unresponsive, many US states have Good Samaritan laws covering rescue. Follow the 911 dispatcher's instructions.
- Prevent it on your end: put your phone or bag in the back seat so you always open the rear door — "look before you lock."
🌡️ Heat exhaustion vs. heat stroke — know the difference
Heat exhaustion is your body struggling; heat stroke is your body failing. The single most important line: confusion, slurred speech, or hot skin without sweat = call 911. Heat stroke can kill or cause permanent damage within 30 minutes.
| Sign | Heat exhaustion — act now | Heat stroke — call 911 |
|---|---|---|
| Skin | Cool, pale, clammy — heavy sweating | Hot, red, dry or damp — sweating may have stopped |
| Body temperature | Normal or slightly elevated | 103°F (39.4°C) or higher |
| Pulse | Fast but weak | Fast and strong (pounding) |
| Mental state | Tired, dizzy, headache, possible fainting | Confusion, slurred speech, loss of consciousness |
| Other signs | Nausea, muscle cramps, weakness | Seizures possible; may vomit |
| What to do | Move to a cool place, loosen clothing, sip water, apply cool wet cloths. Get medical help if vomiting or symptoms last over 1 hour. | Call 911 immediately. Move the person to a cooler place and lower their temperature with cool cloths or a bath. Do NOT give them anything to drink. |
💧 Hydration that actually works
How much
During activity in the heat, aim for about 1 cup (8 oz) of water every 15–20 minutes — roughly a quart per hour. Sip steadily; chugging more than 6 cups an hour does more harm than good. Don't wait for thirst: by the time you feel it, you're already behind.
Electrolytes matter
Sweating for more than an hour drains sodium as well as water. Plain water plus salty snacks works; sports drinks help during long sessions. Muscle cramps are often the first sign you've replaced water but not salt.
What to skip
Alcohol dehydrates you and blunts your sense of overheating — save it for after sundown. Very sugary drinks slow fluid absorption. A quick self-check: pale-yellow urine means you're fine; dark yellow means drink up.
Frequently asked questions
What heat index is dangerous?
The NOAA scale flags a heat index of 90°F as Extreme Caution (heat cramps and heat exhaustion possible), 103°F as Danger (heat exhaustion likely, heat stroke possible), and 125°F or above as Extreme Danger (heat stroke highly likely). But heat illness can occur at lower values too, especially during long exertion, for unacclimatized people, or for older adults and children.
Is 100 degrees too hot to run?
For most people, yes — a heat index of 100°F falls in the Extreme Caution to Danger range, where heat exhaustion is a real risk during sustained exercise. If you must train, run before sunrise or after sunset when the heat index is lower, cut your pace significantly, shorten the session, and carry water. Racing or hard interval work in those conditions is not worth the risk.
What's the difference between temperature and heat index (feels like)?
Air temperature is what a thermometer reads in the shade. The heat index (or feels-like / apparent temperature) combines temperature with humidity — and in Open-Meteo's version, also wind and sunshine — to estimate what your body actually experiences. Humid air slows sweat evaporation, your main cooling mechanism, so 90°F at 70% humidity can feel like 105°F and carries the higher risk.
How hot does a parked car get?
On an 80°F day, a closed parked car reaches about 99°F in 10 minutes, 109°F in 20 minutes, and over 120°F within an hour. Cracking the windows barely changes this. That's why children and pets should never be left in a parked car in warm weather, even briefly.
What are the first signs of heat exhaustion?
Heavy sweating with cool, pale, clammy skin; dizziness; headache; nausea; muscle cramps; a fast but weak pulse; and unusual tiredness. If you notice these, stop activity, move to a cool place, sip water, and cool the skin with wet cloths. If symptoms worsen, last more than an hour, or include vomiting, get medical help.
When should I call 911 for heat illness?
Call 911 immediately if someone in the heat becomes confused, slurs their speech, faints, has a seizure, has hot red skin (dry or damp) with a body temperature of 103°F or higher, or stops sweating despite the heat. These are signs of heat stroke, a life-threatening emergency. While waiting, move them somewhere cooler and cool them with water — but do not give a confused or unconscious person anything to drink.
How much water should I drink in extreme heat?
When active outdoors in the heat, about one 8-oz cup every 15–20 minutes (roughly a quart per hour) is the CDC/OSHA guideline. Drink on a schedule rather than waiting for thirst. If you're sweating for over an hour, add electrolytes — salty snacks or a sports drink — because water alone can't replace lost sodium.
Do fans help during a heat wave?
Only up to a point. Fans help sweat evaporate, but once indoor air rises above roughly 90°F, a fan mostly blows hot air at you and can even accelerate heat gain — especially for older adults who sweat less. In that situation, air conditioning, a cool shower, wet cloths, or a public cooling center are the effective options.
Who is most at risk in extreme heat?
Adults over 65, babies and young children, pregnant people, outdoor workers, athletes, people with heart, lung, or kidney conditions, and anyone on medications that affect fluid balance or heat regulation (like diuretics or beta-blockers). People without air conditioning and those who live alone are at particular risk — most US heat deaths happen indoors.
How accurate is this forecast?
The data comes from Open-Meteo, which blends national weather models (including NOAA's) into an hourly forecast. The feels-like temperature is a model estimate for your location's coordinates — conditions in direct sun, on asphalt, or inside a vehicle can be substantially hotter. Always follow official National Weather Service warnings for your area.