[jcranmer]

From my limited exposure to the HPC groups at the labs, there's a mixture of languages in use. It seems that modern C++ is the dominant language for a lot of new projects--some of the people I talked to were working on libraries that aggressively used C++11/C++14 features.

The biggest challenge the national labs face is that there's not really any budget (or appetite) to rewrite software to take advantage of hardware features (particularly the GPU-based accelerator that's all the rage nowadays). You might be able to get a code rewritten once, but an era where every major HPC hardware vendor wants you to rewrite your code into their custom language for their custom hardware results in code that will not take advantage of the power of that custom hardware. OpenMP, being already fairly widespread, ends up becoming the easiest avenue to take advantage of that hardware with minimal rewriting of code (tuning a pragma doesn't really count as rewriting).