Components — overview & catalog

A forecast is a graph of components. Each component is a versioned, schema-declared unit that states its inputs, outputs, parameters, platform needs, the Cylc fragment it owns, and (for plugins) its prerequisites. List what is available on your install:

nwp-compose components list          # core + discovered plugins
nwp-compose components list --json   # machine-readable

The catalog

Component	Role	Path	Fan-out	Notes
data_ingest	ingest	shared	—	Unified GFS/RAP downloader (dispatches on data_source).
subset_grib	preprocess	shared	—	wgrib2 bbox subsetter; optional in the ungrib graph.
ungrib	preprocess	WRF + MPAS	—	GRIB2 → WPS intermediate; needs a data_ingest upstream.
metgrid	preprocess	WRF	—	metgrid.exe; needs geogrid + ungrib.
geogrid	sub-workflow	WRF	—	One-shot WPS geogrid; publishes geo_em.d??.nc.
mesh_gen	sub-workflow	MPAS	—	One-shot MPAS static mesh; publishes .static.nc + partitions.
init_atmosphere	model init	MPAS	—	ICs (init_case 7); needs ungrib.
lbc	model init	MPAS	—	LBCs (init_case 9); needs init_atmosphere + ungrib.
real	model init	WRF	—	real.exe IC+LBC generation; needs metgrid.
mpas_run	model run	MPAS	—	atmosphere_model; emits a per-fhr completion message.
wrf	model run	WRF	—	wrf.exe; emits a per-fhr completion message.
mpassit	postprocess	MPAS	✓	Native → regular grid, per forecast hour.
upp	postprocess	MPAS/shared	✓	UPP GRIB2 conversion, per forecast hour.
archive_s3	archive	MPAS/shared	✓	S3 upload, per forecast hour.
housekeeping	housekeeping	shared	—	Daily (P1D) prune of work dirs.
data_assimilation	reserved	—	—	Slot reserved in the schema; referencing it is a hard error today.

The two model paths

MPAS — data_ingest → [subset_grib →] ungrib → init_atmosphere → lbc → mpas_run → mpassit → upp → archive_s3, with mesh_gen as a once-only sub-workflow.

WRF — data_ingest → ungrib → metgrid → real → wrf → [upp], with geogrid as a once-only sub-workflow. ungrib and upp are shared between the paths.

You declare presence; the tool proves the graph

You list which components are present and how they connect; nwp-compose derives the Cylc graph from each component’s declared requires_upstream and refuses any workflow where a required upstream is missing, an any_of is unsatisfied, or a forbidden component is present. See the warning catalog for the soft checks layered on top.

Fan-out families

mpassit, upp, and archive_s3 are fan_out_compatible: one instance per forecast hour, triggered by the model’s per-fhr completion message, with concurrency capped per family. This is how per-output-file post-processing scales without writing 50 near-identical task stanzas by hand.

Extending with plugins

Drop a directory with component.yaml + template.cylc.j2 (+ optional namelist/task templates) into the plugin path; it is auto-discovered and listed alongside core components. Plugins are sandboxed — schema and templates only, no arbitrary code at generate time — and declare their requires: so nwp-compose doctor and the validator can check prerequisites.

Troubleshooting

Each golden-path component ships a TROUBLESHOOTING.md next to its component.yaml, following a strict 5-section template (Symptoms / Diagnose / Recover / Blast radius / Escalate). These will be mirrored into per-component pages in this section.

Next

• Namelist dual-mode
• Warning catalog