How HeatCue decides your band
From two readings to one verdict, and where the lines sit.
Updated:
HeatCue starts with two readings for your spot, air temperature and relative humidity. A published method folds them into WBGT, the number you see on the Now screen.
The engine behind the bands
WBGT stands for wet bulb globe temperature, a close cousin of plain wet bulb but not the same thing. Wet bulb asks one narrow question, how cool sweat can get you, so it reads low in dry heat even when the air is dangerous. WBGT rolls air temperature and humidity into one number for how hard the heat is on your body, so sport and workplace heat guidance is written against it. HeatCue computes a shade approximation from the same two readings, the BoM and ACSM method. You read WBGT, and the verdict runs on it.
Where the lines sit
Safe ends at 28. Caution runs from 28 to 30. Danger runs from 30 to 32. Extreme starts at 32. Those are degrees Celsius of effective WBGT (82, 86, and 90 degrees Fahrenheit), and they follow published categories used in sport and workplace guidance.
| Band | WBGT °C | °F |
|---|---|---|
| Safe | < 28 | < 82 |
| Caution | 28 – 30 | 82 – 86 |
| Danger | 30 – 32 | 86 – 90 |
| Extreme | ≥ 32 | ≥ 90 |
Each step up means the heat is harder to shed. The band word and its shape marker carry the verdict, so you never have to judge a raw number in the heat.
The at-risk and dog profiles
Small bodies, older bodies, and hard effort all lose ground to heat sooner, and dogs cool only by panting. So the profiles shift the reading before banding, about 2 °C (4 °F) for the at-risk profile and 3 °C (5 °F) for a dog. Same weather, an earlier verdict.
One honest limit
The readings assume shade. Direct sun adds heat the method does not see. In open sun, act one band earlier.
HeatCue shows conditions and general guidance. It is an awareness tool, not medical advice.