Heat Compass

About this app

Heat Compass turns the official military heat-flag system into a personal heat-safety coach. It computes WBGT (wet bulb globe temperature), the standard used by the U.S. Marine Corps and occupational safety programs, from live weather for your location, then tells you plainly what the conditions mean and what to do about them. KNOW THE FLAG - Live WBGT and the five-color heat flag (White, Green, Yellow, Red, Black) for where you are right now - Work-rest guidance for each flag: how long to work, how long to cool down - 7-day forecast with heat flags, so you can plan the week - Nearby weather stations, and transparency about which station your reading came from STAY AHEAD OF DEHYDRATION - A daily water goal derived from the heat, your activity level, and optionally your body weight - One-tap drink logging with reminders that adapt to the heat flag - An "I'm outside" mode that tightens reminders while you are exposed - Track drinks for family members or a work crew with household tagging - Guidance is capped at safe intake rates, because drinking too much is also dangerous GET WARNED EARLY - Proactive heat-risk alerts: the app periodically checks conditions and warns you when the flag climbs, even when the app is closed - A pavement heat check that estimates surface temperature, useful for dog owners and hot-surface work PRIVATE BY DESIGN No account and no sign-in. Your hydration log, profile, and settings stay on your device. Your location is used to fetch weather for where you are and is not stored on our servers. No ads, no tracking, free. A NOTE ON SCOPE Heat Compass provides general heat-safety guidance based on published heat-stress doctrine. It is an aid for planning, not a medical device, and it does not replace occupational safety programs, OSHA requirements, or your own judgment.

Corrected WBGT accuracy. Heat Compass was under-reading WBGT in hot, dry, sunny conditions - the exact weather where heat is most dangerous. In one Sacramento reading it showed a Green flag where a WBGT meter reads Black. If you used Heat Compass this summer in dry heat, your flag may have been too low. The calculation now uses the Liljegren (2008) model, the method NIOSH references for deriving WBGT from weather data. It solves the natural wet bulb and black globe from full energy balances instead of estimating them, and uses exact sun geometry from your local forecast. Also in this release: - Hydration guidance no longer contradicts itself. The hourly target now respects what the flag and your workload require, and never falls below it because your daily total looks on track. - Hydration needs follow the flag. They previously opened at a placeholder value and only moved when the weather changed. - The flag now refreshes on its own every 10 minutes and when you reopen the app, instead of waiting for you to pull to refresh. - Chart legend uses the same White/Green/Yellow/Red/Black names as the rest of the app. "SAFE" is gone - a green flag is low risk, not safe. - Removed the pavement heat checker.

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1. First observed Aug 12, 2026 · 2:51 AM Free