Aurora 1.5 is a major extension of Microsoft’s Aurora Earth System foundation model that adds 22 more weather variables relevant to energy, agriculture, transport, and climate risk, along with hourly temporal resolution and probabilistic ensemble forecasting. Released as open source on GitHub with model checkpoints on Hugging Face, Aurora 1.5 enables researchers and developers to use, evaluate, and build on the model. Developed by Microsoft Weather as an extension of the original model from Microsoft Research AI for Science, Aurora 1.5 shows how frontier research can move into broader use. Aurora is a foundation model for the Earth system developed by Microsoft Research AI for Science, first introduced in 2024 and published in Nature in 2025. Aurora 1.5 adds one of the most requested capabilities from users: ensemble forecasting, which runs multiple simulations to show the range and likelihood of possible outcomes. Aurora 1.5 builds on Microsoft Research’s scientific foundation with new product engineering, cloud infrastructure, managed access, and decision-support capabilities.