shadeway.today

Weather apps report air temperature, but that number explains surprisingly little about how a walk actually feels. What your skin registers is closer to what climatologists call mean radiant temperature — direct sunlight, plus light reflected off pavement and walls, plus heat radiating back off every hot surface around you. Air temperature barely changes from one side of a street to the other; radiant temperature can swing by tens of degrees between the sunny side and the shaded one.

That's most of the effect right there — enough on its own to pull radiant temperature down by up to 16°C under a single tree, and measurements in some city streets have found shaded spots running 30°C cooler by this measure than sunny ones a few meters away. A building's shadow works the same way as a tree's — direct comparisons find the two land in about the same range — and the measured "feels-like" temperature (human biometeorologists call it PET) drops by something in the range of 7 to 15°C — without the air temperature moving by a single degree.

Not all shade earns that number equally, either. Bigger, taller canopies cool more — a global analysis across 596 cities found each extra meter of tree height corresponds to roughly 0.16°C less surface heat on average — which is why this app tries to use a tree's actual crown size where the map records it, rather than treating every dot marked "tree" as identical.

None of it holds still, either. The sun crosses the sky at a steady 15° an hour, so a stretch of pavement that's fully shaded at ten in the morning can be in direct sun an hour later — and the lower the sun sits, the more a shadow's length swings for the same small change in its angle. That's why this app doesn't just remember "this street has trees" — it computes the sun's exact position for your date and time and traces the real geometry of every shadow from there.

You don't even need a heatwave to feel the difference. A walk to the shops, to a meeting, or pushing a stroller simply feels different the moment you're not standing directly under the sun — less UV hitting your skin, fewer squinted eyes, more attention left for the city instead of the sky. Shade isn't a workaround for bad weather; it's a measurable, physical thing you can route around, the same way you'd route around traffic.