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NBM forecast guidance

Available since v0.20.0 as noaa:nbm. The National Blend of Models is NOAA's statistically blended, bias-corrected forecast guidance, issued hourly and built from many models rather than run as one. Its GRIB2 core output lives in the anonymous noaa-nbm-grib2-pds S3 bucket as blend.YYYYMMDD/HH/core/blend.tHHz.core.fFFF.<region>.grib2, one whole file per run, forecast hour, and region, each beside a .grib2.idx sidecar. No AWS credentials or SDK are needed. The adapter shares its run selection with HRRR; read that page's explanation of runs, cycles, and valid times first.

Runs, cycles, and valid times

NBM runs every hour; cycle (required) names the run's UTC hour, 0 to 23. The query window selects runs by initialization time, inclusive, and spans at most one day; a bare date as both bounds is that whole day and selects its cycle run. A window containing no cycle initialization is rejected before any request.

Times are UTC

Timestamps without a timezone are treated as UTC, including queries built directly in Python; explicit offsets are converted to UTC. Both bounds are inclusive. A date alone as the end means the last instant of that UTC day, so a window from 2024-05-07 to 2024-05-07 is that whole day; give the end a time to stop earlier. See time and place.

forecast_hour (required) is an integer, a list, or a comma-separated string from 1 to 264; there is no hour 0. Which hours a run publishes depends on the cycle, so the adapter does not encode the schedule: an hour the run lacks is reported by name after the listing. Observed for the CONUS files of 2024-05-06:

Cycles Hours
00, 12 UTC Hourly to 36, then every 3 hours to 192
06, 18 UTC Hourly to 36, every 3 hours to 192, then every 6 hours to 264
01, 13 UTC Hourly to 173
07, 19 UTC Hourly to 152
Every other cycle Hourly to 36 or 37, every 3 hours to about 190, then every 6 hours to about 262, ending on a synoptic valid time

Asset times record each file's valid time, initialization plus forecast hour.

Regions and sizes

region Grid Size (2024-05-06 20Z, f001)
co (default) 2.5 km Lambert conformal CONUS, 2345 × 1597 points 171 MB
ak Alaska 52 MB
hi Hawaii 6 MB
pr Puerto Rico about 3 MB
gu Guam 0.6 MB

The qmd percentile files and the text bulletins are out of scope. A CONUS hour holds 300 messages, so whole-file downloads add up fast: prefer messages. variables, text, and geographic constraints are rejected because the server cannot subset the files.

Fetching selected messages

messages fetches only the GRIB2 messages you name, as byte ranges of the object, exactly as the HRRR guide describes. NBM index lines carry a further text for ensemble statistics and probability thresholds, so TMP:2 m above ground names the value alone and TMP:2 m above ground:1 hour fcst:ens std dev names its spread. Selectors observed in the 2024-05-06 20Z CONUS f001 file:

Field messages
2 m temperature TMP:2 m above ground
2 m dewpoint DPT:2 m above ground
1-hour precipitation APCP:surface:0-1 hour acc fcst 
uv run usdata fetch noaa:nbm \
  --start 2024-05-06T20:00Z --end 2024-05-06T20:00Z \
  -p cycle=20 -p forecast_hour=1,2,3 -p messages="TMP:2 m above ground" --dry-run

Each 2 m temperature message is about 1.5 MB of the 171 MB file. The fetched file is the messages concatenated, which is itself a valid GRIB2 file, and its lockfile entry pins the byte ranges and the object's ETag (ADR 0028).

Reading fields

The grib extra opens a file with FetchedAsset.open_grib2(select=...) as an xarray Dataset; a file fetched with messages is already a selection and opens without select. The CONUS grid is Lambert conformal, so the reader attaches two-dimensional latitude and longitude coordinates of shape (1597, 2345); longitudes use the 0–360 convention. The 2 m temperature opens as 2t in kelvin. See the reader reference for the extra's platform support.

Archive coverage

The bucket's day prefixes begin on 2020-05-18, but the core/ layout this adapter reads begins with the 12 UTC run of 2020-09-29; earlier runs hold a grib2/ layout of master files that is not reachable here. Windows before that run are rejected before any request. The NODD registry entry documents public cloud access, and the NBM product page describes the blend.

See the service research notes for dated upstream probes.

Metadata sources

Every value in the catalog entry's resolution, cadence, citation, terms, variables, and limits comes from one of these pages. A field the agency does not publish is left empty rather than estimated.

  • Resolution: the 2345 × 1597 Lambert grid at 2.54 km, read from a fetched CONUS message with ecCodes on 2026-09-16, and the NBM product page.
  • Updates, citation, and terms: the NODD registry entry and the NOAA Open Data Dissemination statement it quotes.
  • Forecast-hour schedule: bounded listings of every cycle of blend.20240506/ on 2026-09-16, tabulated above.
  • Variables: the messages table above. A file holds hundreds of fields, so the entry lists only the ones this guide and the example use.
  • Longest query window: MAX_WINDOW in usdata.providers.noaa.hrrr, which this adapter shares through ModelRuns.
  • Latency is empty: NODD states no lag between a run's initialization and its appearance.

All NOAA datasets.

Reference

noaa:nbm · Released · Included since usdata 0.20. National Blend of Models.

At a glance

  • Files: GRIB2
  • Selection: Regional core files, whole or by named GRIB2 message, chosen by run initialization window, cycle hour, forecast hours, and region
  • Required inputs: Both timestamps, cycle, and forecast_hour
  • Open locally: usdata[grib] · Reader guide
  • On usdata.dev: NBM forecast guidance, with a walkthrough

Parameters

Pass these as --param name=value to the CLI, as params: entries in a manifest, or as keyword arguments to build_query.

Parameter Meaning
cycle Required UTC initialization hour of the run, 0 to 23.
forecast_hour Required forecast hour(s): an integer, list, or comma-separated string, 1 to 264; hourly to 36, then every 3 hours, then every 6, on a schedule that varies by cycle.
messages Optional GRIB2 messages to fetch instead of the whole file, spelled as the object's wgrib2 .idx sidecar spells them: 'SHORTNAME:level text', such as 'TMP:2 m above ground', with an optional ':step text'; one value, a list, or a comma-separated string. Short names are upper case and both fields match exactly.
region Grid: co (default, 2.5 km CONUS), ak (Alaska), hi (Hawaii), pr (Puerto Rico), or gu (Guam).

Variables

Variable Units Meaning
2t K 2 m temperature
2d K 2 m dewpoint temperature
tp kg/m2 Total precipitation accumulated over the step

Catalog facts

  • Availability: since 0.20
  • Domain: Weather models
  • Spatial resolution: 2.5 km Lambert conformal CONUS grid, 2345 x 1597 points; separate Alaska, Hawaii, Puerto Rico, and Guam grids
  • Temporal resolution: Hourly runs; forecast hours hourly to 36, then every 3 hours to about 190, then every 6 hours to 264, on a schedule that varies by cycle
  • Updates: Hourly
  • Longest query window: 1 day
  • Terms of use: https://www.noaa.gov/information-technology/open-data-dissemination
  • Citation: NOAA National Blend of Models (NBM) was accessed on [date] from https://registry.opendata.aws/noaa-nbm
  • Catalog date range: 2020-09-29 to open-ended
  • Coverage varies by station, product, and date; the range above does not guarantee observations.
  • Upstream documentation
  • License: US Government Work (public domain)
  • Transport: s3
  • Adapter: usdata.providers.noaa.nbm:Nbm