What's the flag condition right now?
Check your location
Search any city or place to get the current reading here, without leaving this page.
What the flag actually encodes
A flag is a shorthand for a work/rest ratio and a water intake, indexed to WBGT rather than to air temperature — because the thing that limits a body under load is whether it can still shed heat, and that depends on humidity, wind and radiant load as much as on the thermometer.
That is also why a flag condition is not transferable between contexts without thought. The cycles assume a particular workload; heavier work at the same flag is a different exposure. Our guidance shows the standard band, and the app can escalate it for an individual’s own situation — it never relaxes below the published band.
Where a modelled reading helps, and where it doesn’t
It helps for planning: seeing the day’s arc before you build the schedule, checking a training area you’re travelling to, or knowing whether the evening window is genuinely cooler. It gives you a consistent number across sites, which a single kit at a single point cannot.
It does not replace the instrument where the instrument is required. A modelled WBGT is derived from gridded weather; a kit sitting on the actual training area captures that ground, that surface and that shade. When a standing order says measure, measure.
Acclimatization is part of the plan, not a footnote
Heat adaptation takes one to two weeks and decays during time away. New arrivals, personnel returning from leave, and anyone transitioning from a cool climate are all operating without it — which is why the opening days of a cycle carry disproportionate risk. See why the first hot week is the most dangerous.
Screening guidance only. This is not an official flag determination and does not supersede your command’s or department’s standing orders, local policy, or a required on-site measurement. Heat stroke is a medical emergency — cool first, transport second.
What to do at each level
| Level | WBGT | Guidance |
|---|---|---|
| Safe | below 64°F | No flag — routine operations. No flag — general awareness only; keep water intake up. |
| Caution | 64–73°F | No flag — keep water intake up. No flag / white — routine work; keep water intake up. |
| Moderate | 73–82°F | Green–yellow flag — build in rest cycles. Green → yellow flag: about 50/10 to 40/20 min work/rest. |
| High | 82–90°F | Red flag — 30/30 work-rest. Red flag near ~31 °C: 30 min work / 30 min rest per hour. |
| Extreme | 90–95°F | Black flag — suspend strenuous PT. Black flag (≥32 °C): 20 min work / 40 min rest, ~1 qt water/hour; strenuous PT suspended. |
| Lethal | 95°F and up | Black flag — halt exertion. Black flag — exertion halted; get people to cooling. |
Screening guidance shown for an acclimatized person at moderate workload. Add your own situation in the app for a personalized read — it only ever makes the guidance stricter, never looser.
Common questions
What are the WBGT flag conditions?
The flag system maps WBGT bands onto work/rest cycles and water intake, escalating from no flag through green, yellow, red and black. The US Army's TB MED 507 is the reference most commonly used, and the guidance shown on this page follows that framework. Individual commands and departments may run stricter local rules.
Is this the same as an on-site WBGT kit reading?
No. Our value is modelled from weather data for your coordinates. Where a unit or department requires a measured on-site WBGT to set the flag, that instrument reading is the one that governs. Use this to plan the day, pick the window, and know what to expect before the kit comes out.
Why do the limits assume trained, monitored people?
The flag system was built for populations that are screened, acclimatized, supervised and have medical support close by. Those assumptions do a lot of work. Applying the same cycles to unacclimatized personnel, or to anyone without monitoring, removes the margin the system depends on.
How does gear change the calculation?
Body armour, turnout gear, CBRN suits and similar impermeable equipment block evaporation, which is the body's principal cooling mechanism. Standard practice is to apply a WBGT adjustment for encumbering clothing — the effective heat stress is higher than the ambient reading. Treat the number here as the ambient case and adjust upward for gear per your own policy.
Does the guidance change at night?
The wording does — after dark it stops referring to shade and shifts to what actually applies. The physiology doesn't get a discount: humid nights with little wind clear heat poorly, and hard surfaces hold the day's load for hours, so night training on a paved area is not the same as night training on grass.
Other audiences
Asphalt runs far hotter than the air. Check the ground temperature where you are before you walk.
Work/rest guidance from the live heat-stress reading, for crews, supervisors and safety officers.
Activity modification for training and competition — plus your state's own high-school WBGT policy.