[MansurJisan-NCO]

Description

For STOFS-2D-Global ops mode, build_sfcf_forcing replaces segments fcst1 (0-120 h hourly) and fcst2 (120-180 h 3-hourly) with one segment fcst: 181 hourly records over 0-180 h. It is used for a single 180 h forecast run.

• Hours 0-120, and every 3rd hour after, are copied byte for byte from the GFS sfcf records.
• Hours 121-179 not divisible by 3 are filled by linear interpolation between the bracketing 3-hourly records, streamed two files at a time. ADCIRC interpolates meteorology linearly in time between snapshots, so the forcing at every model step matches the operational fcst2 to float32 rounding.
• The later bracketing file must have the same lat/lon values as the earlier one, and the forcing manifest lists both bracketing files for each interpolated record.
• ncst is unchanged.

Type of change

• New feature (non-breaking change which adds functionality)

Change characteristics

• Changes outputs (values, COMOUT files or names, archives)? YES, STOFS-2D-Global ops mode only: <RUN>_fcst.{221,222,225}.nc replaces the fcst1/fcst2 files.
• Breaking change to existing functionality? NO. The fcst1/fcst2 segments were only used by ops mode, which changes with the paired nos-workflow PR.
• Requires a nos-utils submodule bump (nos-workflow) or a paired nos-workflow change (nos-utils)? YES, the paired nos-workflow PR; merge this one first.
• Requires new or regenerated fix files on the machine? NO
• Requires a re-prep or a new hotstart before the next cycle? NO
• Machines affected: both

How has this been tested?

• pytest: 1280 passed, 9 skipped.
• New tests (small synthetic sfcf files):
  • 181 records;
  • exact copies at native hours (0, 7, 120, 123, 126, 180);
  • weights 1/3 and 2/3 at hours 121 and 122;
  • fill values preserved;
  • the manifest lists both bracketing files;
  • a bracketing file on a shifted grid fails with no partial files;
  • a missing f180 waits, then fails, leaving no partial files.
• Independent review: GO.
• Not yet run on WCOSS2.

Checklist

• Dependent PRs merged and published (nos-utils before any submodule bump)
• pytest suite passes
• Existing operational behavior preserved, or the change is called out above
• No edits to a shared FIXofs while it is cycling
• Self-review done; yaml comments and docstrings updated where behavior changed
• No markdown files added to the repo (this template is the only exception)

[Copilot]

🟡 Changes recommended

The bracket-grid validation checks only array shape, allowing incompatible equal-sized grids to be interpolated silently.

1 open finding

• Grid validation checks shape but not coordinate values · New

What changed in this PR

Consolidates STOFS-2D-Global forecast forcing into one hourly 180-hour segment.

Changes:

• Replaces fcst1/fcst2 with fcst.
• Interpolates non-native hours after forecast hour 120.
• Adds interpolation, fill-value, manifest, and failure tests.

File	Description
nos_utils/​forcing/​adcirc_met.py	Implements unified forecast generation and interpolation.
tests/​test_adcirc_met.py	Tests the new forecast behavior.

🧠 Review effort: Balanced

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