SurfaceCast: Surface TempSupport
SurfaceCast estimates how hot ground, walls and roofs get, using the hourly forecast for the place you pick. If something is not behaving the way you expect, the notes below cover the questions we hear most. Anything else, just email us — we read every message.
FAQ
Why is the temperature different from what my thermometer says?
SurfaceCast calculates an estimate from a physical model; it does not measure anything. Real surfaces vary with thickness, construction, moisture, reflections from nearby buildings, local wind and the exact shape of the shadow falling on them. Treat the numbers as a well-reasoned guide, not a reading.
Can I use this to decide whether a surface is safe to touch or walk on?
No. SurfaceCast is built for observation and learning, and it deliberately does not make safety judgements. If that decision matters — for a child, a dog's paws, or your own hands — measure the surface with an infrared thermometer instead.
Why does a surface stay hot after it goes into shade?
That is the point of the app. Sunlight stops instantly, but materials with thermal mass hold the heat they have absorbed and release it slowly. Thick concrete and bitumen can stay well above air temperature for hours after the sun leaves them, while thin metal cools within minutes.
Why does grass stay so much cooler than bitumen?
Two reasons. Grass is lighter in colour, so it absorbs less sunlight, and water evaporating from the blades and the soil carries heat away. Together these keep living grass remarkably close to air temperature even in strong sun.
Where does the weather data come from?
Hourly forecasts come from Open-Meteo. SurfaceCast sends only the coordinates of the place you choose, rounded to roughly a kilometre, and nothing else.
Does it work without a connection?
Yes, using the last forecast it downloaded for that place. The app tells you when it is showing cached data, so you know the figures may be out of date.