AI summary · arXiv: 2611.09573v1 · physics.ao-ph

Half-precision inference of AI weather prediction models: negligible loss of skill at a fraction of the cost

Stefan Siegert
Original paper Submitted to arXiv on 06 Nov. 2026 40 pages, 15 figures, 9 tables. Code: https://github.com/sieste/ai-nwp-fp16 License: not stated (all rights reserved) Also in: fr

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The essentials

Running five AI weather models with network computations in fp16 and physical states in fp32 preserves forecast skill closely while reducing runtime and energy use.

Based on the abstract only: check the details in the original paper.

Question

Can half-precision inference reduce the computational cost of AI weather prediction without materially degrading forecast skill? The study also examines where reduced precision affects model accuracy and compares fp16 with bf16 and 8-bit quantisation.

Method

The author ran Aurora, Pangu-Weather, FourCastNet, SFNO and FastNet on a single 16 GB GPU from 52 initial dates in 2024, comparing fp32 and fp16 forecasts against ERA5. The physical state and its normalisation and denormalisation remained in fp32; experiments also tested sensitivity to reduced precision and compared speed, energy use, ensemble properties, bf16 and 8-bit quantisation.

Findings

  • Result With the physical state and its normalisation and denormalisation kept in fp32, fp16 changed global RMSE by at most 1.4%, and by about 0.5% or less for four models.
    See the passage in the paper
    With the state, its normalisation and denormalisation in fp32, running the network in fp16 changes the global RMSE by at most 1.4%, and by about 0.5% or less for four of the five models, equivalent to less than one hour of lead time up to day 8 and at most two hours at day 10.
  • Result The study found no systematic regional, scale, or storm-type pattern in forecast differences, apart from a small tropical penalty in FourCastNet.
    See the passage in the paper
    The differences show no systematic pattern by region, scale or for tropical and extratropical storms, apart from a small tropical penalty in FourCastNet, and fp16 leaves the CRPS, spread and calibration of Aurora's ensemble almost unchanged.
  • Result A 10-day fp16 forecast was 1.3–3.5 times faster and used 1.4–3.7 times less energy than fp32.
    See the passage in the paper
    A 10-day forecast in fp16 is 1.3-3.5 times faster than in fp32 and uses 1.4-3.7 times less energy.
  • Result The study reports that layer sensitivity varied among models, and that bf16 and simple 8-bit quantisation did not match fp16's accuracy.

Limitations

  • The evaluation covers five publicly available models, 52 initial dates in 2024, and forecasts verified against ERA5; the abstract does not establish performance beyond this scope.
  • The findings apply to an inference setup that keeps the physical state and its normalisation and denormalisation in fp32; converting the whole model is not viable in the reported setup.
    See the passage in the paper
    The physical state must stay in fp32: converting the whole model rounds it in physical units, which in fp16 overflows and in bf16 discards meaningful information.

Why it matters

The authors argue that fp16 network inference, with the physical state kept in fp32, offers a practical way to run AI weather models on a single GPU with little loss of skill and substantially lower cost. Their model-specific sensitivity results caution against assuming reduced-precision rules from other applications will transfer directly.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: AI weather forecasting half precision fp16 inference forecast skill computational efficiency

Read further

  • Comprehensive Summary
  • Layman's Summary
  • Blog article
  • Original abstract
The paper investigates whether AI weather prediction models can run in half precision without materially reducing forecast skill, while lowering computational costs. Publicly released models generally use 32-bit floating-point (fp32) weights and run in fp32 by default, although modern GPUs can compute faster using 16-bit formats. The study compares fp32 and fp16 inference across five publicly available models: Aurora, Pangu-Weather, FourCastNet, SFNO, and FastNet. The authors ran the models on a single 16 GB GPU, using 52 initial dates from 2024, and verified their forecasts against ERA5. A central finding is that the physical atmospheric state, along with its normalisation and denormalisation, should remain in fp32. Converting the entire model and state to reduced precision can cause problems: fp16 may overflow when representing values in physical units, while bf16’s lower precision may discard meaningful information. In the tested setup, the neural network runs in fp16 while state-handling operations remain in fp32. With this approach, fp16 changed global root-mean-square error by no more than 1.4%. For four of the five models, the change was about 0.5% or less. The authors equate these differences to less than one hour of forecast lead time through day 8 and, at most, two hours by day 10. They found no systematic pattern in skill changes across regions, spatial scales, or tropical and extratropical storms, although FourCastNet showed a small penalty for tropical storms. For Aurora’s ensemble, fp16 left the continuous ranked probability score, ensemble spread, and calibration almost unchanged. The study also reports computational and numerical results. A 10-day fp16 forecast ran 1.3 to 3.5 times faster than its fp32 counterpart and used 1.4 to 3.7 times less energy. None of the tested values exceeded fp16’s representable range of ±65,504; the largest values were 38 to 544 times smaller than that limit. Sensitivity experiments showed that the effects of reduced precision varied across architectures. The first and last layers were influential in some models but not others, and no layer type was consistently sensitive on its own. The abstract also reports that bf16 was as fast as fp16 but less accurate for every model, while simple 8-bit quantisation caused substantially greater skill loss. The authors conclude that, for the models and inference setup they tested, running network computations in fp16 while keeping the atmospheric state in fp32 preserves forecast skill while substantially reducing runtime and energy use. However, the evidence is limited to five models, one 16 GB GPU, 52 initial dates from 2024, and the verification and tests described in the abstract. Because the full paper is unavailable, the exact experimental configuration, statistical uncertainty, and sensitivity-test procedures cannot be assessed. The results support the tested approach, but the abstract alone does not establish that the same trade-offs apply to other models, hardware, forecast periods, or deployment settings.

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Weekly letter Presented in "Climate and Earth this week" of 9 November 2026. Climate and Earth this week: Hidden shortages, spreading fires and signals beneath the surface

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