Wind forecast for your bike route

A weather app says “westerly, 6 m/s”. Whether that's a friend depends on which way you're pointed. Velvind does that sum for the whole route:

• The route becomes a point every 250 metres, each with the compass bearing you'll be riding on.
• At each point, the forecast wind is read at your arrival time, between the hours either side. Wind is interpolated as a vector, so a breeze swinging through north never averages into a direction it never came from.
• The wind is split into a part along the road and a part across it. Over 1.4 m/s along the road against you is a headwind; the same from behind is a tailwind; the rest is crosswind or calm.

The colours follow: green for a tailwind and nothing else, stone for a crosswind or calm, coral for the stretch you'll spend fighting it. The strip under the horizon names its runs in words, so colour never carries the meaning alone.

That's why Velvind reads the wind where you'll be when you're there, not the wind at the start. Kilometre 60 has its own weather.

A headwind makes the ride longer, and then the rest of it meets the weather later. So Velvind times the ride in two passes: first in still air, then with the part of the wind along the road. The app counts a quarter of the forecast wind (shelter, other riders and sitting up in a tailwind take the rest), calibrated against real rides. The headwind calculator shows what that comes to on 10 km.

In a steady wind, a closed loop's headwind and tailwind cancel out whichever way you ride it. What makes a difference is a wind that turns or builds while you're out, or a shower you can dodge. When that happens, Velvind says if the loop is kinder the other way round. Otherwise it says nothing.

• Headwind calculator Minutes lost or gained per 10 km, from the same wind timing as the app.
• Best time to ride Every half hour of the next nine days, read the same way. ⚡ marks the kindest start.
• Riding in wind How much wind is too much, and how to save your legs.