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Yes very good point this to me is one of the most magical elements of this loss how it suddenly makes the model "collapse" on one output and the predictions become sharp.

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Yeah, it's underplayed in the the writeup here but the context here is important. The "sharpness" issue was a major impediment to improving the skill and utility of these models. When GDM published GenCast two years ago, there was a lot of excitement because the generative approach seemed to completely eliminate this issue. But, there was a trade-off - GenCast was significantly more expensive to train and run inference with, and there wasn't an obvious way to make improvements there. Still faster than an NWP model, but the edge starts to dull.

FGN (and NVIDIA's FourCastNet-v3) show a new path forward that balances inference/training cost without sacrificing the sharpness of the outputs. And you get well-calibrated ensembles if you run them with random seeds to their noise vectors, too!

This is a much bigger deal than people realize.

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