Sphere with fins over Roubaix consistent with a helium balloon

Summary

A witness in Roubaix saw a spherical object with fins gliding silently from east to west before climbing vertically and vanishing into a sunny sky. There were no other witnesses. The observer compared it to an inflatable advertising balloon but noted that the westerly wind should have pushed it the other way. However, meteorological data from Lille recorded an easterly wind, consistent with the reported trajectory. Investigators pointed out that surface wind can differ from wind at higher altitude, and the object's erratic movements were coherent with a loose helium balloon.