Heat stress in San Francisco
Cool and foggy most of the year; rare heat spells hit hard because few homes have air conditioning.
Heat stress is low right now — normal outdoor activity is fine.
Live wet-bulb globe temperature via the Liljegren (2008) method · automatically refreshed about every 30 minutes.
View San Francisco on the live mapReading heat stress in San Francisco
Wet-bulb globe temperature (WBGT) is the heat measure that actually tracks danger to the body. Unlike the plain air temperature on your phone, it folds in humidity, wind, and direct sun — the factors that decide whether your sweat can still cool you. It’s the standard the military, athletic associations, and occupational-safety bodies use to call when outdoor activity is no longer safe.
That matters in San Francisco because cool and foggy most of the year; rare heat spells hit hard because few homes have air conditioning. The number above is the live outdoor WBGT for the city right now; tap through to the live map to inspect any neighborhood, scrub the forecast hour by hour, and see the 7-day outlook.
Heat in San Francisco: common questions
What is the WBGT in San Francisco right now?
Right now it's about 57°F WBGT (safe heat stress). This page shows the live wet-bulb globe temperature for San Francisco, California, refreshed automatically about every 30 minutes. Open the live map for an exact reading at your neighborhood and an hour-by-hour forecast.
Why is WBGT more useful than the temperature for San Francisco?
Air temperature ignores humidity, wind, and sun — the things that decide whether heat is dangerous. San Francisco's climate (cool and foggy most of the year; rare heat spells hit hard because few homes have air conditioning.) is exactly why a single "feels-like" or thermometer reading can understate the real risk. WBGT captures all of it in one number.
When is heat most dangerous in San Francisco?
Heat stress typically peaks in the early-to-mid afternoon, when sun load is highest. Plan strenuous outdoor activity for early morning or evening, hydrate ahead of time, and use the forecast scrubber on the live map to find the safest window.
Is WetBulbTracker free to use for San Francisco?
Yes. WetBulbTracker is free, needs no account, and works for anywhere on Earth — not just San Francisco. You can install it to your home screen and even set heat alerts.