Rain you can scrub

The rain overlay used to be one still picture: the latest radar frame from a third-party tile service, shown on the Navigate tab and nowhere else. From today it is a timeline — the last two hours of weather radar as frames you can play, pause and drag through, on the Map tab beside the lean and acceleration HUD, and on Navigate. The frames come from a service of our own, built on the pan-European EUMETNET OPERA radar composite.

What changed for you

Play the rain. Switch on the 🌧 overlay (Settings → Map → Overlays, now called Rain timeline) and a thin bar appears in the bottom band of the map: ▶ plays the frames at one every 0.6 s and holds on the newest before looping; drag anywhere on the track to scrub. The label shows the frame's clock time and how far behind "now" it is — −45 min, −1 h 15 min. A white tick marks the newest observation.

On the Map tab, not just Navigate. The Map tab had no overlay pipeline at all before; it has one now, and the lean slider and the accel card move up out of the bar's way so nothing overlaps (the owner's device pass will settle the landscape details).

Honest about freshness. OPERA publishes a composite every 15 minutes, about 20 minutes behind real time. If our ingest falls three steps behind — the server's beat has died, the publisher is refusing us, the disk is full — a ⚠ appears on the bar rather than a stale picture pretending to be current. The ⟳ button re-reads the frame list; when the capped user-triggered refresh lands it will show next in 6 min instead of failing quietly.

One source, all of Europe. The composite is the merged product of around 170 national radars from Portugal to Finland, on a 2 km grid. The old service had quietly dropped its forecast frames and its terms were for personal use only; it is gone from the app and from the credits page.

How it is built

Phones never talk to a weather upstream. A scheduled task on our server lists the last two hours of composites from the MeteoGate Open Radar Data API, downloads each new Cloud-Optimized GeoTIFF (about 3 MB) from its 24-hour cache, and warps it once to web-mercator — 0.45 s — into an immutable frame on disk. Tiles are rendered from those frames on demand (12–33 ms each, then cached forever, because a frame id names one product time and is never rewritten), with one logarithmic mm/h palette for every source so the picture will not change its look when the nowcast and forecast bands arrive.

The phone reads one small manifest — the ordered frame list, a tile URL template, a legend and a freshness block — and mounts the current frame plus three neighbours on each side as raster layers, switching them by opacity as you scrub. Seven sources on the native bridge at most, however long the timeline gets.

What is next

Two hours of the past is the first band. The plan adds an hourly forecast to +24 h from DWD's ICON-EU model, a nowcast of our own extrapolated from the radar motion, and — for the Nordics — MET Norway's 1 km radar and forecast composited over the European product. The scrubber already has the three bands drawn in, tinted differently, waiting for the frames.

Frames and tiles: /weather/rain/frames.json and /tiles/rain/{frame}/{z}/{x}/{y}.png, documented under Developers → Weather timeline. Radar data © EUMETNET OPERA, via MeteoGate, CC BY 4.0.