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Every channel is keyed by the lowercase ICAO code of an airport. There are three namespaces; the two observation namespaces share one payload shape, while forecasts carry a different one.

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Namespaces

See METAR Observations, D-ATIS Fast Lane and Model Forecasts for the full field reference of each namespace.
The station list grows over time. Subscribing to a channel that doesn’t exist yet simply fails with a channel_format error, so it is safe to probe for a station before you know it is live.

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Last-value replay

Immediately after a successful subscribe, the server replays the most recently cached message for that channel, so a new subscriber gets current state instantly instead of waiting for the next update.
  • Observations are cached for 45 minutes, since new reports typically arrive every 20 to 30 minutes.
  • Forecasts are cached for 12 hours, since a model run is only published every 1 to 6 hours.
A replayed frame carries "cached": true. Never use a cached frame to measure delivery latency.

Next: METAR Observations

See the full field reference for the observation channel.