nClimGrid-Monthly precipitation fixture provenance (#1121)
Per docs/research/nclimgrid-acquisition-and-redistribution.md: a retrieval-pinned
snapshot of a mutable NCEI period-of-record object, not a claim of an immutable
per-month source object.

Source
  endpoint:        https://noaa-nclimgrid-monthly-pds.s3.amazonaws.com/nclimgrid_prcp.nc
  route:           AWS S3 Explorer (NODD dataset noaa-nclimgrid-monthly-pds), Region us-east-1
  object key:      nclimgrid_prcp.nc
  retrieval time:  2026-09-22T21:24:54Z (S3 response Date header)
  size:            1796927222 bytes
  Last-Modified:   2026-09-08T21:23:02Z
  ETag:            "2ad66993ba82dfe27af796d4d37ee7e0"
  x-amz-checksum:  crc32 tTnCCg== (base64) = b539c20a (hex), FULL_OBJECT
  project SHA-256: 85118392e6be2321b76472631290916d45e81865866ee0d950fb1ad9b14b9c44
  full response headers: see the `curl -D` capture retained alongside this run

Native grid (as downloaded, full period of record)
  variable: prcp, units millimeter
  dims: time=1580 (1895-01 to 2026-08), lat=596, lon=1385
  bounds: lat 24.56-49.35 N, lon -124.69 to -67.02 W (CONUS bounding box)

Selected time coordinates and reduction recipe (benchmarks/cli_multiprocessing.py prepare)
  1. sel(time=slice("1981-01-01", "2024-12-31")) -> 528 months, matching #1097's
     CHIRPS series length so only spatial scale changes between the two issues
  2. land mask = finite cells of the first prepared time step (1981-01); every
     other time step forced to that same mask
  3. zeros -> 0.01 mm (gamma has no support at zero)
  4. cast to float32, written with no inherited packing encoding
  5. dims reordered to (lat, lon, time) -- the CLI's shared-array transport
     (climate_indices.__main__._TRANSPORT_DIMENSIONS) accepts only this order;
     the xarray/Dask harness transposes on read, so it accepts either order

Prepared fixture
  path (external, not committed): nclimgrid_prcp_1981_2024.nc
  sha256: e88478c201fce89994e03937db1a13e34cd0c9c929578c5fe925d5a69a7c3cb2
  grid: time=528 lat=596 lon=1385
  land=469758 of 825460 cells (56.9%); masked (non-CONUS/ocean)=355702 (43.1%)
  zeros replaced with 0.01 mm: 2291008

Citation (NCEI-specified format; subset and access date filled in per the
research doc's instruction -- this is a reduced/modified subset, not the whole
unmodified dataset)
  Vose, Russell S., Applequist, Scott, Squires, Mike, Durre, Imke, Menne,
  Matthew J., Williams, Claude N. Jr., Fenimore, Chris, Gleason, Karin, and
  Arndt, Derek (2014): NOAA Monthly U.S. Climate Gridded Dataset (NClimGrid),
  Version 1. Monthly precipitation, CONUS, 1981-01 to 2024-12, reduced to a
  land-masked, zero-adjusted float32 grid for this benchmark. NOAA National
  Centers for Environmental Information. DOI:10.7289/V5SX6B56. Accessed
  2026-09-22.

Notices (NODD dataset entry, registry.opendata.aws/noaa-nclimgrid)
  - This is a reduced and modified derivative of the NOAA NClimGrid dataset,
    not original, unaltered NOAA data.
  - No claim or implication of NOAA endorsement or affiliation.
