Worldwide rainbow forecast
Know when the light will bend.
Bowcast reads a 40 member weather ensemble through the optics of how rainbows actually form: sunlit rain, with the sun below 42 degrees, seen from the right angle. It predicts the chance of a rainbow, hour by hour, seven days out, anywhere on Earth.
The physics, honestly
A rainbow needs three things to line up at once.
Rain in front, sun behind
There has to be falling rain in one part of the sky and clear sun in the other. Bowcast checks both across the ensemble.
The geometry of the bow
A rainbow only forms when the sun sits lower than 42 degrees above the horizon, so timing near sunrise and sunset matters most.
Looking the right way
The bow appears opposite the sun, centered on your antisolar point. Bowcast tells you which way to face.
The app is the almanac, made live.
The same reading you see here is the reading on the map, on the live board, and on every city page. Glance to learn whether, where, and when to look. Reveal the model when you want the evidence.
Now on the App Store
The same instrument, in your pocket.
Bowcast for iPhone runs the same forecast as this site and adds what a browser tab cannot: alerts that arrive while the app is closed, a forecast that offers to follow you when you travel, and sighting reports that wait for signal.
Pick a threshold from 5% to 95%. When your place crosses it, the notification says how likely, when, and which way to face.
Open it somewhere new and it offers, once, to move your forecast there. It never asks for background location.
Seen or not seen, filed anonymously with coordinates rounded to about a kilometre, sent when you next have a connection.
Free · No account · iPhone, iOS 16.4 or later
