To your knowledge is there anybody working on a “littering the globe with huge quantity of cheap self-contained sensors” kind of project? Or is that the kind of work best done from the air or from orbit?

I am no authority to speak about this - but I believe expanding sensors and improving on data gathering is a continuous and on-going effort (e.g., weather station on ships, airplanes, stations deployed on sea etc.). Better weather satellites are also a thing. But then there is just so much more that could be done and all these data-points are still unevenly distributed (e.g., planes and ships follow routes). Weather models are improving quite a bit “behind the scenes” but again - I think we are far away from getting anything reliable for several days into the future; not to speak months or years.

Here is a nice interview highlighting a couple of improvements people are driving for a niche sport weather forecast: https://magazine.weglide.org/skysight-interview-matthew-scut...