The mechanics

How it works

A weather app tells you what the sky is doing at home. Velvind answers a different question: what will the sky be doing where you are, when you get there, for every kilometre of a ride that moves. Here is the reading, start to verdict.

1. 1

   Your route, every 250 metres

   Whatever you bring in (a Strava route, a GPX, TCX or FIT file, a Ride with GPS link), Velvind resamples it into evenly spaced points, one every 250 metres. Each carries its distance, elevation, the grade of the road under it and the compass bearing you'll be riding on. That bearing is what makes wind mean something later. Climbing is counted from the original track, lightly smoothed, rather than from the resample, so the headline metres agree with your head unit.

2. 2

   Timing from your speed, the climbs and the wind

   You give Velvind your usual average speed. It turns that into a speed on the flat using how hilly your own routes are, then walks the route point by point: climbs slow you with the gradient, descents speed you up to at most 65 km/h, and any stops you add are counted where they are. A second pass feeds part of the headwind or tailwind into the speed, so a ride into the wind takes longer, as it does. Each ride can be Easy, Usual or Hard, and an e-bike setting keeps the speed up on climbs. The result is an arrival time for every point on the route, not just the finish.

3. 3

   One forecast per patch of sky

   The route is reduced to weather cells about 11 km across (a 0.1° grid), with an hourly forecast for each from Open-Meteo: nine days ahead in the app, up to sixteen in the web planner. In the Nordics, the app reads the next two hours from MET Norway's radar nowcast instead. Because each cell arrives as a whole hourly series, the forecast doesn't depend on when you leave: change the departure or the speed and the ride re-reads at once, with nothing new to download.

4. 4

   Weather at the minute you arrive

   For every point, Velvind reads the forecast at that point's arrival time, interpolating between the two hours either side. Wind is interpolated as a vector, so a breeze swinging through north between 09:00 and 10:00 never averages into a direction from nowhere. This is the difference between “wind from the west today” and the wind you'll actually meet at km 60.

5. 5

   Wind, resolved against you

   A westerly is a fact; whether it's a friend depends on which way you're pointed. Each point's wind is split against your bearing into a headwind and a crosswind part, then called head, cross or tail. That is the colour along the route: green for a tailwind and nothing else, stone for a crosswind or calm, coral for the stretch you'll spend fighting it. The verdict says which half of the ride gets it: a tailwind out, a headwind home.

6. 6

   Daylight from the sun's geometry

   Sunrise, sunset, civil dawn and dusk and golden hour are computed from the sun's position for the day and place you're riding, then laid against your arrival times. If the ride crosses sunset, Velvind tells you when you'll need lights, as a clock time.

7. 7

   The kindest start

   Velvind runs the whole reading again for every half-hour start across the next nine days and marks the kindest with ⚡. It weighs a headwind harder than a tailwind, and counts rain on the road, gusts, cold and riding in the dark; only a daylit start that isn't rough can win. It reuses the forecasts already in hand, so the scan costs nothing and answers at once.

8. 8

   One word when it turns

   Add a ride and Velvind keeps checking its forecast, every 15 minutes. You hear only when the reading turns (a headwind home where there was none, rain where it was dry): by email, and by push on the phone once the ride is within 36 hours. Each has its own switch. If nothing changes, nothing arrives.