---
id: "2024-12-04-gencast-ensemble-weather"
url: "https://postcutoff.com/e/2024-12-04-gencast-ensemble-weather/"
as_of: "2026-11-13T13:49:00+01:00"
date: "2024-12-04"
date_precision: day
category: science
importance: 3
confidence: high
status: [Result confirmed]
verification: Peer-reviewed
sources: 2
editor: human editor
human_review: null
version: "2026-10-04"
---

As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/e/2024-12-04-gencast-ensemble-weather/

# GenCast: diffusion-based ensemble forecast beats ECMWF's ENS on 97% of targets

GenCast (Nature, Dec 2024) is a diffusion model producing probabilistic 15-day ensemble forecasts. It beat ECMWF's ENS, the leading operational ensemble, on 97.2% of 1,320 targets and on 99.8% at lead times beyond 36 hours, generating a 15-day ensemble member in about 8 minutes on one TPU.

## Key facts
- 97.2% of 1,320 targets better than ENS; 99.8% beyond 36 h
- Better prediction of extreme weather, tropical-cyclone tracks and wind-power output
- Code and weights released for research

## What happened

DeepMind applied image-style diffusion to the atmosphere, sampling many plausible futures rather than one.

## Why it matters

Ensembles drive decisions about extreme-weather risk. AI now leads here too, feeding into the WeatherNext models used by forecasters.

## Your AI and this story

- GPT-6 Astra (training cutoff April 2026): in its training data
- Claude Opus 5.5 (training cutoff June 2026): in its training data
- Gemini 4 Hydrogen (training cutoff March 2026): in its training data
- Grok 4.7 (training cutoff May 2026): in its training data

## Sources

1. [Probabilistic weather forecasting with machine learning (Nature)](https://www.nature.com/articles/s41586-024-08252-9) (nature.com, paper)
2. [DeepMind: GenCast](https://deepmind.google/blog/gencast-predicts-weather-and-the-risks-of-extreme-conditions-with-sota-accuracy/) (deepmind.google, official)

## Changes

- 2026-09-29 (filed): Created

## Related

- 2026-08-06: [DeepMind open-sources WeatherNext 2 and WeatherNext Cyclones with a Nature paper showing ~1 extra day of hurricane warning](https://postcutoff.com/e/2026-08-06-weathernext-open-source/index.md)
- 2023-11-14: [GraphCast: ML weather model beats the world's best physics-based 10-day forecast on 90% of targets](https://postcutoff.com/e/2023-11-14-graphcast-weather/index.md)