Forecast Extension Specification

• Title: Forecast
• Identifier: https://stac-extensions.github.io/forecast/v1.0.0/schema.json
• Field Name Prefix: forecast
• Scope: Item, Collection
• Extension Maturity Classification: Proposal
• Owner: @m-mohr

This document explains the Forecast Extension to the SpatioTemporal Asset Catalog (STAC) specification.

• Examples:
  • Item example: Shows the basic usage of the extension in a STAC Item (todo)
  • Collection example: Shows the basic usage of the extension in a STAC Collection (todo)
• JSON Schema (todo)
• Changelog (todo)

Fields

The fields in the table below can be used in these parts of STAC documents:

• Catalogs
• Collections
• Item Properties (incl. Summaries in Collections)
• Assets (for both Collections and Items, incl. Item Asset Definitions in Collections)
• Links

Field Name	Type	Description
forecast:datetime	string	The forecast datetime, which must be in UTC. It is formatted according to RFC 3339, section 5.6.
forecast:horizon	string	The time between the reference datetime and the forecast datetime. Formatted as ISO 8601 duration, e.g. PT6H for a 6-hour forecast.
forecast:accumulation_period	string	If the forecast is not only for a specific instance in time but instead is for an accumulation over a certain period you can specify the length here.Formatted as ISO 8601 duration, e.g. PT3H for a 3-hour accumulation. If not given, assumes that the forecast is for an instance in time as if this was set to P0TS (0 seconds).

One of the fields forecast:datetime or forecast:step is REQUIRED!

Additional Fields from other extensions

Field Name	Type	Description
datetime	string	REQUIRED. The reference datetime. It follows the definition in the STAC Common Metdata. Alternatively, start_datetime and end_datetime can also be used.
expires	string	The datetime until the forecast is valid or gets superseded by a new forecast. It follows the definition in the Timestamps Extension.
deprecated	string	Set this to true if a newer version of the forecast is available. It follows the definition in the Version Extension.

It is also recommended to implement the Version Extension and use it to "deprecate" old forecasts and link between them using the given relation types.

Media Types

You can use any file format, but here is a list of common media types for forecast assets that have not been listed yet in the list of common media types in STAC:

Type	Description
application/wmo-GRIB2	GRIB2 file (usually with the file extension .grb2 or .grib2)
application/netcdf	NetCDF file (usually with the file extension .nc)

Contributing

All contributions are subject to the STAC Specification Code of Conduct. For contributions, please follow the STAC specification contributing guide Instructions for running tests are copied here for convenience.

Running tests

The same checks that run as checks on PR's are part of the repository and can be run locally to verify that changes are valid. To run tests locally, you'll need npm, which is a standard part of any node.js installation.

First you'll need to install everything with npm once. Just navigate to the root of this repository and on your command line run:

npm install

Then to check markdown formatting and test the examples against the JSON schema, you can run:

npm test

This will spit out the same texts that you see online, and you can then go and fix your markdown or examples.

If the tests reveal formatting problems with the examples, you can fix them with:

npm run format-examples