There's a long explanation but the summary is that FORTRAN was one of the first languages that targeted the highest computing demands so there was functional an

There's a long explanation but the summary is that FORTRAN was one of the first languages that targeted the highest computing demands so there was functional and financial interest in making it highly performant. Hardware was often designed around FORTRAN and a tight relationship over decades between those who wrote FORTRAN, those who wrote compilers and tooling for FORTRAN, and those who sold hardware for FORTRAN to run on in large high-performance/supercomputing worked together make things run stupidly efficiently and had decades to do so. C has some similar legacy but came a little later to the game and wasn't as intuitive to people driving the money in computing as they were with FORTRAN. It's also heavily optimizeable from a performance perspective but often missed the initial buy in and momentum, though developed much of its own. So FORTRAN has a lot of investment and strategic advantages to be used for things like weather modeling, at least for specific underlying libraries. Modern work tends not to start from greenfield in FORTRAN, it often starts in C or really a high language like Python to provide theoretical proof of concept and just write/use wrappers to highly optimized codebases like those for FORTRAN for the numeric fundamentals in the model. Lots of scientific glue code these days with not a lot of stuff making it into optimization levels like you see in BLAS, LAPACK, ScaLAPACK, etc.