AFAIK, weather models use a mesh which is much coarser in z-direction. So it's a factor of 4, not 8. Another issue is that increased resolution isn't much helpf

AFAIK, weather models use a mesh which is much coarser in z-direction. So it's a factor of 4, not 8. Another issue is that increased resolution isn't much helpful unless you also have higher resolution initial data (measurements). Finally, handling uncertainty means you have to do multiple runs. I believe the wall clock runtime of a single weather simulation has been stable at about 30 mins. for decades now, and increases in computing power is used to either refine the grid or to run more simulations with slightly different initial data. Then there's also the problem of postprocessing and analysing the huge amounts of data you end up producing.