Wind arrows commonly called wind barbs have not been the choice of Windy developers. Wind barbs are a graphical way to show both the direction and speed of wind. They were specially useful when weather maps were black printed maps, but windbarbs are still used nowadays even with numerical maps.
Wind barbs show the wind direction as wind particles do in Windy.
Concerning the wind speed, wind barbs give a 5kt speed span and are usually displayed at grid points of the weather model, for example with a 22km distance for GFS, 9km for the ECMWF model…
With interpolated speed, Windy brings more speed details as displayed by the weather picker. Interpolating wind speed with barbs is possible but surely not easy.
We must admit that the colour scale of wind speed is not very precise. This is reason why I have customised on my side the speed scale and calibrated it in Beaufort units.
At a glance I know the direction and the wind force.
You can in the same way customise the color scale to get a 5kt steps color scale.