Heat Tracker

What this is showing

Wet Bulb Globe Temperature (WBGT) is what sports physiologists use to gauge heat stress in distance runners, since it combines air temperature and humidity with the radiant heat load a body absorbs outdoors — a fuller picture than air temperature alone. A true WBGT reading comes from a black-globe thermometer plus wind and solar sensors; this page instead uses the Australian Bureau of Meteorology’s outdoor approximation, which estimates the same value from temperature and humidity: WBGT ≈ 0.567·Ta + 0.393·e + 3.94, where eis vapor pressure derived from relative humidity. It’s a solid stand-in when there’s no physical sensor on hand, but it doesn’t yet account for wind speed or direct sun, so on very sunny, still days the real WBGT may run a bit higher than shown here.

The flag categories and training notes follow the American College of Sports Medicine’s WBGT guidelines: green flag is a green light for whatever’s on the schedule, yellow flag calls for easing off intervals, tempo, and other structured hard efforts while easy mileage stays fine, red flag means shifting those hard efforts to a treadmill or a cooler window of the day, and black flag is the point where outdoor training itself carries real heat-illness risk. The 48-hour outlook is there to help pick which window — this afternoon, tomorrow morning — is the better time for a track session or long run.

This is general sports-science guidance, not a substitute for a coach’s judgment — heat illness can escalate quickly during hard efforts, so when conditions sit near a flag boundary, it’s worth erring conservative and listening to how the body actually feels that day.