https://wasatchweatherweenies.blogspot.com/2020/04/the-power-of-data-assimilation.html

As of 23 March, the ECMWF reported a 65% reduction in
European aircraft weather observations and a 42% global reduction.

Based on early studies, the ECMWF suggests that removing all aircraft
observations from their data assimilation system results in a degradation of
short-range temperature and wind forecasts at jet-stream level of 15% and
surface pressure forecasts of 3%. The former illustrates why it is advantageous
for aviation companies to provide such observations for weather prediction,
since the improvement in forecast skill reduces fuel consumption through better
route planning and may also improve passenger comfort through better turbulence
forecasts.

Modern data assimilation truly is an incredible scientific marvel. Without it,
numerical weather prediction would not be possible and any great global forecast
system has a great data assimilation system.

Thanks to Ron Gleason.