Rain Viewer: How I Built a Global Weather App
I didn’t set out to build a weather startup — I just wanted to know exactly when it was going to rain.
Living outside the US, I was frustrated by how limited most weather apps were. They’d show vague forecasts like “scattered showers,” but no live radar, no real-time animations, no storm movement. Meanwhile, American apps had all the eye-candy: moving precipitation maps, storm tracks, even alerts for rotating cells.
I thought: This data must exist. Why can’t the rest of the world see it?
That curiosity led to a late-night side project that eventually became Rain Viewer — today a weather radar app with 4+ million users in 90+ countries, known among weather geeks, hikers, and storm chasers for its precision and global reach.
Why Build Another Weather App?
Let’s be honest: the weather app market is brutally competitive. Big tech and national agencies dominate. But here’s the catch: most apps are hyper-localized, and global radar coverage was practically non-existent.
That was our opening.
Rain Viewer became the first mobile app to aggregate radar from 1,000+ stations worldwide, including regions usually “off the map” for popular apps — parts of Asia, and the Middle East. We turned scattered national data into a single interactive global radar, updated every 5 minutes.
Today, if you open Rain Viewer in Croatia or Iceland, you can see exactly where rain is falling — even above a specific building.
Behind the Scenes: From Raw Radar to a Smooth Map
Radar data is messy. Every country has its own formats, refresh rates, and quirks. Some post live data via APIs, others upload GIFs to FTP like it’s 1998.
We built a backend that ingests and normalizes all this chaos, then serves clean tiles for our mobile apps. Our iOS and Android apps (Swift + Kotlin) share a custom radar rendering engine that can smoothly animate storms even on budget phones — because performance is everything when a thunderstorm is moving your way.
Growing Rain Viewer: Community and Product
Some of RainViewer’s early traction came from unexpected corners of the world.
Central Europe turned out to be a hidden gem: countries like Poland and Romania had reliable radar coverage, but almost no consumer apps were using that data.
These markets taught us a core lesson: go where your users have weather pain points, not just where you expect high app-store traffic.
In Europe and the US, competition is tougher. But we found that simplicity + accuracy always wins. Our users love:
Fast, clear radar animations
Hyper-local precipitation alerts
Premium tools like storm tracking, 2-hour precipitation forecasts, and historical radar maps
Lessons for Indie Developers
If you’re thinking of building a consumer tool like Rain Viewer, here’s what worked for us:
Solve a real frustration – I built Rain Viewer because I needed it.
Find the gap – Big players ignored global radar coverage. That was our wedge.
Start small and iterate – We began with radar in Europe, then expanded worldwide.
Monetize later – Free-first worked; we added premium subscriptions ($4.99–$19.99) for power features.
Make UX a priority – If your app isn’t instantly clear, users will bounce.
From Side Project to Global App
We’re still a fully remote team of 12, without billion-dollar satellites — but Rain Viewer now serves millions of people checking weather before a commute, a hike, or a storm chase.
What started as a personal annoyance has grown into a global weather platform, giving everyday users access to professional radar data — and helping them literally see the rain above their own homes.
You can find out more about my app (as well as being a weather enthusiast) on the website – rainviewer.com
