Getting Started

aifs-modal uses four external services. Set them up once in the order below, then jump to the Your First Forecast notebook.

1. Modal

Modal is the serverless GPU platform that runs AIFS inference. The Starter plan gives you $30/month in free credits — a 96-hour forecast costs roughly $0.05.

1. Create a free account at modal.com.

2. Install the CLI and authenticate:

   pip install modal
   modal setup
   

2. Forecast output storage

Forecast outputs are stored as Icechunk repositories in object storage. Tigris is the recommended default: it is co-located with Modal’s primary region, so data transfer between them is fast and free, and the free tier includes 5 GB/month.

1. Create a free account at tigrisdata.com.

2. Create a bucket and generate an access key pair (access key ID + secret access key).

Any backend supported by Icechunk works — AWS S3, Cloudflare R2, Google Cloud Storage, Azure Blob Storage, or Earthmover ArrayLake.

3. Initial conditions source

aifs-modal supports four IC sources, selected with the source= argument of run_forecast:

source	Credentials	Coverage	Notes
"ifs-arraylake" (default)	Earthmover account + Brightband subscription	~last 15 days	Fastest and most reliable; used in Your First Forecast
"ifs-ekd"	None	~last 2 years	No credentials, but frequent 503 Slow Down errors make it unreliable
"era5-arco"	None	1979 — ~5 days ago	ERA5 reanalysis; used in Jet-stream free run and Heatwave reforecast
"era5-cds"	~/.cdsapirc	1979 — ~5 days ago	ERA5 via Copernicus CDS; slower than era5-arco

Note

ERA5 publication lags real time by about 5 days, so the ERA5 sources are suitable for hindcasts and reforecasts but not for operational use.

To set up the default ifs-arraylake source:

1. Create a free account at app.earthmover.io.

2. Subscribe to the Brightband ECMWF IFS dataset on the marketplace (free).

3. Copy your API token from the Earthmover dashboard.

4. Modal secrets

aifs-modal reads credentials from three named Modal secrets. Create them once with the CLI:

# Tigris / S3-compatible object storage (forecast outputs)
modal secret create aws-credentials \
  AWS_ACCESS_KEY_ID=<key> \
  AWS_SECRET_ACCESS_KEY=<secret> \
  AWS_REGION=auto

# Earthmover ArrayLake (only required for the ifs-arraylake IC source)
modal secret create arraylake-api-token \
  ARRAYLAKE_API_TOKEN=<token>

# HuggingFace (model weights download)
modal secret create huggingface-secret \
  HF_TOKEN=<token>

Secret name	Key(s)	Purpose
aws-credentials	AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION	Forecast output storage
arraylake-api-token	ARRAYLAKE_API_TOKEN	ifs-arraylake IC source
huggingface-secret	HF_TOKEN	Downloading AIFS model weights

Secrets are stored in your Modal workspace and injected automatically into every function call — no need to re-create them.

Notebooks

• Running your first serverless AIFS forecast on Modal
• AIFS Extended Free-Running Forecast: Mid-February to End of May 2026
• June 2025 European Heatwave Ensemble Reforecast
• CMIP6-style SST patching: “what-if” scenario forecasts
• A1 – Preparing Reference Data for Verification
• A2 – Initial-Conditions Ingestion Benchmark