Is it safe outside right now?
HeatCue turns temperature, humidity, and sun into one plain verdict for where you are. Built on wet bulb and WBGT, the numbers heat safety actually runs on.
DangerTime to find shade.
Heat isn’t just temperature.
Humidity keeps sweat from cooling you, so heat hits harder than the number says.
The same 31 degrees can be an easy afternoon or a dangerous one. Humidity decides, so HeatCue runs on wet bulb and WBGT instead of the plain forecast.
Learn the science →How it works
Weather in, one verdict out
- 1
It reads the air
Live temperature, humidity, and sun for your area, as close as weather data allows. Readings are outdoor, and you pick open sun or shade.
- 2
It runs the science
A published method folds them into WBGT, the measure sport and workplace heat guidance is written against.
- 3
You read one word
Safe, Caution, Danger, or Extreme, with a plain sentence on what to change. One second, and you know.
Safe
Good to be outside.
Sweat is cooling you the way it should.
Caution
Take water and breaks.
Sweat evaporates slower now, so you heat up faster.
Danger
Time to find shade.
Cooling down gets hard. Heat builds even at rest.
Extreme
Stay inside if you can.
Sweat barely evaporates. Your body cannot shed this heat for long.
Limit
Stay in cooled air.
Sweat can no longer cool anyone enough. Heat builds even resting in shade.
A fifth band sits past Extreme. Limit appears only when the wet bulb passes 31 °C (88 °F), the point where sweat can no longer cool anyone, even resting in shade. Almost nowhere on Earth has ever reached it, so most people will never see this band.
Sun or shade
The same street, read two ways
Standing in open sun is not the same as standing in the shade. HeatCue reads both, so you can see what stepping under a tree actually buys you. Every reading starts in open sun; one tap shows the shade.
After dark, sun and shade read the same.
See the heat coming.
Pro adds more warning, more places, more profiles.
- The current verdict for your location: WBGT, wet bulb, and the risk band.
- Sun or shade: the same weather read two ways, so you know what the shade buys you.
- The full Learn library and the heat calculator.
- Threshold alertsProA heads-up before it gets dangerous
- The 7-day heat outlookProPlan runs, hikes, and walks
- Home screen widgetsProYour heat band without opening the app
- Every place you care aboutProHome, the trailhead, grandma’s town
- ProfilesProEach with its own heat limits
ProFeatures marked Pro come with HeatCue Pro. Pro is a subscription, with a one-time Permanent unlock if you prefer to pay once. Prices show on the App Store.
Questions, answered
Is HeatCue free?
Yes. The heat verdict for your location is free, always: WBGT, wet bulb, the risk band, and the sun or shade switch. HeatCue Pro adds alerts before the heat, the 7-day outlook, home screen widgets, more places, and profiles, including ones you build yourself.
What is wet bulb temperature?
The lowest temperature your sweat can cool you to. In dry air it sits far below the thermometer; in humid air the two converge and sweating stops working. Past a wet bulb of about 31 degrees Celsius (88 degrees Fahrenheit), heat builds in a resting body even in deep shade.
What is WBGT?
Wet bulb globe temperature: one number for how hard the heat is on your body, folding air temperature and humidity together with a published method. Sport and workplace heat guidance is written against WBGT, and it is the headline number in HeatCue.
Why can a mild forecast still be dangerous?
Humidity. When the air already holds plenty of water, sweat sits on your skin instead of evaporating, and you stop cooling. A humid 31 degrees Celsius is harder on your body than a dry 40. Wet bulb and WBGT see that; the plain forecast does not.
Where do the readings come from?
Public weather data for your area, read as an outdoor estimate for where you are. You choose whether that is open sun or shade, and the number moves with your choice.
Is HeatCue medical advice?
No. HeatCue shows conditions and general guidance drawn from published heat categories. It is an awareness tool, not medical advice. Anyone confused, fainting, or getting worse after cooling down needs emergency care.
Does HeatCue account for standing in direct sun?
Yes. Every reading starts in open sun, where the solar load is part of the number. One tap shows the same weather in the shade, so you can see what the shade is worth. After dark the two read the same.
Know before you go.
HeatCue is on iPhone in eleven languages. The verdict is free; Pro adds the foresight.