Skip to content

gefs.md

Latest commit

 

History

History
245 lines (171 loc) · 19.7 KB

gefs.md

File metadata and controls

245 lines (171 loc) · 19.7 KB
Raw

GEFS (Global Ensemble Forecast System)

What this model is

The Global Ensemble Forecast System (GEFS) is the United States' primary global ensemble numerical weather prediction system, operated by NOAA's National Centers for Environmental Prediction (NCEP).

GEFS is the ensemble counterpart to the deterministic GFS, built on the same FV3-based atmospheric model and the same Earth system framework, with 31 ensemble members (1 control + 30 perturbed) running 4× daily. It produces probabilistic medium-range forecasts for most cycles and extends to 35 days at the 00 UTC cycle, providing the United States' operational sub-seasonal forecast guidance.

GEFS is also a contributing member to the North American Ensemble Forecast System (NAEFS), the 557th WW GEPS multi-model ensemble, and the HGEFS hybrid physics-AI grand ensemble — making it one of the most heavily-used ensemble forecast products in operational meteorology.

The current operational version is GEFSv12 (operational since 23 September 2020), with GEFSv13 under development for joint deployment alongside GFSv17 (proposed for October 2026).

Who runs it

  • Organization: NOAA / National Centers for Environmental Prediction (NCEP)
  • Country / region: United States

What area it covers

  • Coverage: Global

Basic details

  • Model type: Global ensemble NWP
  • Model system / core: Unified Forecast System (UFS) atmospheric model with FV3 (Finite-Volume Cubed-Sphere) dynamical core
  • Dynamical formulation: Non-hydrostatic, on a cubed-sphere finite-volume grid; semi-Lagrangian vertical coordinate
  • Convection-allowing: No (deep convection is parameterized at ~25 km resolution)
  • Ensemble size: 31 (1 control gec00 + 30 perturbed gep01–gep30), plus derived geavg (mean) and gespr (spread) products. A separate GEFS-Aerosols run produces the chem/ stream to 5 days with the GOCART aerosol chemistry component (one-way coupled) — see Product inventory.
  • Perturbation method: Initial-condition perturbations from the EnKF ensemble, combined with stochastic physics (SPPT, SKEB, SHUM) for model-uncertainty representation
  • Native horizontal resolution: ~25 km (C384 cubed-sphere grid)
  • Public output grids (live-verified 2026-07-31):
    • 0.25° — pgrb2s product only, and only to +240 h
    • 0.5° — pgrb2a and pgrb2b products, full forecast length
  • Vertical levels: 64 (hybrid sigma-pressure)
  • Forecast length:
    • 35 days (840 h) for the 00 UTC cycle (sub-seasonal range) — verified: all 33 prefixes (31 members + mean + spread) run the full 840 h, not a subset
    • 16 days (384 h) for 06, 12, and 18 UTC cycles
  • Temporal output resolution: 3-hourly to +240 h, then 6-hourly to the end of the run (verified uniform across pgrb2a/pgrb2b; pgrb2s is 3-hourly throughout its shorter 240 h span)
  • Update frequency: 4× daily (00, 06, 12, 18 UTC)
  • Coupled wave model: WAVEWATCH III ensemble, replacing the previous standalone Global Wave Ensemble — documented separately as GEFS-Wave

⚠️ The 0.25° grid is not the primary output. Earlier revisions of this entry described 0.25° as "primary output" and 0.5° as an "alternative resolution." Live enumeration shows the opposite emphasis: the 0.25° pgrb2s product carries only 38 records per step and stops at +240 h, while the full-field pgrb2a (85 records) and pgrb2b (505 records) products are 0.5° only and run the full length. pgrb2s is a small curated surface subset, not a high-resolution version of the full output.

Initial conditions

GEFS is initialized from 6-hour EnKF forecasts drawn from the same 80-member EnKF ensemble that informs the GFS hybrid 4DEnVar analyses (see GDAS in the GFS entry).

The initial condition files are publicly distributed — see The init/ stream below.

What it provides

Probabilistic global forecasts of:

  • Temperature, wind, pressure, and humidity (surface and upper-air)
  • Precipitation amount, rate, and type, with probability-of-exceedance guidance derivable from the member spread
  • Cloud cover, convective indices, and boundary-layer diagnostics
  • Aerosol fields (from the separate GEFS-Aerosols chem/ run)
  • Wave height, period, and direction (from the coupled WAVEWATCH III ensemble)
  • Ensemble mean (geavg) and spread (gespr) as pre-computed products alongside the raw members

Product inventory

Live-verified against gefs.20260731/ on 2026-07-31. "Extended" = 00 UTC (840 h); "standard" = 06/12/18 UTC (384 h).

atmos/ — the ensemble proper

Directory Grid Prefixes Records/step Steps (ext / std) Size/step Volume (ext cycle)
pgrb2sp25 0.25° 33 (31 members + geavg + gespr) 38 81 / 81 (capped at +240 h) 17.8 MB 47.6 GB
pgrb2ap5 0.5° 33 85 181 / 105 12.3 MB 88.4 GB
pgrb2bp5 0.5° 31 (members only — no mean or spread) 505 181 / 105 97.7 MB 548.9 GB
init native cubed-sphere 31 members × 13 files — 1 (analysis) — 121.8 GB

chem/ — GEFS-Aerosols, a single unperturbed run

Directory Grid Files Records/step Steps Size/step
pgrb2ap25 0.25° gefs.chem.tCCz.a2d_0p25.fFFF.grib2 32 41, 3-hourly to +120 h 23.3 MB
pgrb2ap5 0.5° gefs.chem.tCCz.a3d_0p25.fFFF.grib2 — 41, 3-hourly to +120 h 179.8 MB

chem/ is not a 32nd ensemble member in any usable sense — it is a single deterministic aerosol run with no member dimension, its own file-naming scheme, a 5-day cap, and a different directory. Note the naming inconsistency: the file in pgrb2ap5/ is named a3d_0p25 despite sitting in the 0.5° directory.

wave/ — gridded/ and station/, documented in GEFS-Wave.

Total volume: ≈ 2.64 TB per day (115,708 objects) — 864 GB for the 00 UTC extended cycle and ~593 GB for each of the other three. pgrb2bp5 alone is 549 GB of the extended cycle. This makes GEFS by a wide margin the largest single dataset in this catalog, roughly 2.4× HRRR's daily volume.

The init/ stream

atmos/init/{c00,p01…p30}/ holds the initial conditions for every member as NetCDF: gfs_ctrl.nc (7.5 KB) plus gfs_data.tile1–6.nc and sfc_data.tile1–6.nc (580 MB each) on the native cubed-sphere tiles. 403 objects, 121.8 GB per cycle, at every one of the four cycles.

This makes the full 31-member cubed-sphere initial state publicly available — unusual, and comparable to the HRRRDAS ensemble backgrounds in the HRRR buckets. It is DA/model-input machinery rather than forecast output, but it is gridded and openly distributed. Present on all three clouds.

Relationship to other models

  • GFS: Deterministic counterpart, sharing the FV3 dynamical core and GDAS analysis infrastructure
  • NAEFS: Multi-center ensemble combining GEFS with Canadian GEPS and (for the 557th WW GEPS) FNMOC NAVGEM ensemble; provides bias-corrected probabilistic guidance across North America
  • 557th WW GEPS: U.S. Air Force statistical multi-model ensemble that uses GEFS as one of its three contributing single-center ensembles
  • HGEFS: Hybrid grand ensemble combining the 31 GEFS members with 31 AIGEFS AI-based members, providing a 62-member physics-plus-AI ensemble
  • AIGEFS: AI-based ensemble counterpart trained to emulate GEFS behavior
  • GEFS-Wave: The one-way-coupled WAVEWATCH III ensemble in the wave/ subtree
  • GFSv17 and GEFSv13: Co-developed; GEFSv13 will be the ensemble counterpart to the proposed coupled Earth-system GFSv17

Reforecasts

A 30-year GEFSv12 reforecast dataset supports calibration and statistical post-processing, and is distributed from its own AWS bucket:

Live-verified structure (2026-07-31):

  • 21 year-directories, 2000–2020, one initialization per day at 00 UTC (366 dates in 2000, 365 in 2019)
  • 5 members per date (c00 + p01–p04) — not the 31 of the real-time system
  • Split into two lead-time blocks, Days:1-10 and Days:10-16
  • Organized per-variable, not per-step (e.g. apcp_sfc_2000010100_c00.grib2, 27 MB), each with a .idx sidecar

⚠️ The 2020/ directory contains a single misfiled date. It holds only 2010070100/ — a 2010 initialization sitting under the 2020 year prefix. Anyone enumerating by year will find 2020 effectively empty and may silently lose that date. Whether real 2020 reforecasts exist elsewhere is unconfirmed (TBD).

Note the colon in the Days:1-10 path component. This is legal in S3 keys but requires URL-encoding in HTTP requests and breaks naive local-filesystem mirroring on Windows.

The reforecast underpins many calibrated ensemble products including those in the NAEFS bias-correction system.

Data availability

  • Is the data free? Yes (no registration, no API key)
  • License: Public domain (U.S. government work; CC0-equivalent). Distributed via NOAA Open Data Dissemination (NODD): data are open to the public and may be used as desired. NOAA requests attribution, prohibits stating or implying NOAA endorsement or affiliation, and requires that modified data not be presented as unaltered NOAA data.
  • Is the data downloadable? Yes
  • Data formats: GRIB2 with .idx index sidecars (forecast fields); NetCDF (the init/ stream); gzipped TAR and BUFR (soundings, NOMADS only)

Distribution channels

1. NOMADS (NCEP operational distribution) — real-time, 4-day rolling window

https://nomads.ncep.noaa.gov/pub/data/nccf/com/gens/prod/
  gefs.YYYYMMDD/{00,06,12,18}/{atmos,chem,wave}/
    atmos/{bufr,init,pgrb2ap5,pgrb2bp5,pgrb2sp25}/

Retention observed on 2026-08-01: 4 days (gefs.20260729 through gefs.20260801).

NOMADS carries a bufr/ subtree that no cloud mirror has. Under atmos/bufr/ sit per-member gec00/, p01/–p30/, and avg/ directories of exploded station soundings, alongside 32 bundled ge{c00,p01…p30,avg}.tCCz.bufrsnd.tar.gz files (~76 MB each) and an ls-l manifest. None of it exists on AWS, Azure, or GCS — all three show only init/, pgrb2ap5/, pgrb2bp5/, and pgrb2sp25/ under atmos/, and ls-l returns HTTP 404 on each.

With a 4-day NOMADS window and no cloud copy, GEFS station soundings are effectively unarchived — the same pattern documented for RAP, and the inverse of HRRR, where GCS is the only archival route to them.

Both the OPeNDAP (/dods/) and FTPPRD (ftpprd.ncep.noaa.gov, ftp.ncep.noaa.gov) routes were retired on 23 February 2026 under SCN 25-81 and SCN 25-82 respectively. This matters for NAEFS, whose entry still lists the nomads.ncep.noaa.gov/dods/gens_bc OPeNDAP endpoint for bias-corrected GEFS.

2. AWS Open Data (NODD) — real-time + the deepest archive

Archive: gefs.YYYYMMDD/ from 2017-01-01 to present — 3,500 directories with zero calendar gaps across the full span. Note that the pre-2020-09-23 portion is GEFSv11 at a different resolution and directory layout.

3. Google Cloud Storage (NODD) — real-time + GEFSv12-era archive

Archive: 2,137 directories from 2020-09-25 — i.e. starting two days after the GEFSv12 implementation, so the GCS archive is GEFSv12-only by construction. That is arguably cleaner than AWS's mixed-version archive for anyone who wants a single-version dataset, but it means the 2017–2020 GEFSv11 period is AWS-only.

⚠️ GCS is missing 315 .idx sidecars per cycle, all in the wave/gridded/ subtree — specifically the mean, spread, and prob derived products (105 each). Every GRIB2 data file is present, and the atmos/ and chem/ trees are complete. The same systematic-missing-.idx pattern documented for RAP on GCS. Byte-range subsetting of the wave derived products will not work there.

4. Microsoft Azure (NODD) — real-time, 90-day rolling window

Live window on 2026-08-01: 92 days (gefs.20260502/ → gefs.20260801/) — the same ~90-day pattern as the Azure GFS, RAP, and CFSv2 containers.

Within its window, Azure is the most complete of the three mirrors — object counts match AWS exactly (36,223 for the 00 UTC cycle), including all the .idx sidecars GCS lacks.

⚠️ Azure enumeration gotcha. As with the Azure GFS container, a single un-paginated list request for prefix=gefs. returns zero results with a NextMarker — it looks exactly like an absent stream. Follow NextMarker to exhaustion before concluding a prefix is empty.

5. NCEI — long-term archive

Cross-cloud equivalence

The GRIB2 forecast files are byte-identical across all three clouds. For gefs.20260731/00/atmos/pgrb2sp25/geavg.t00z.pgrb2s.0p25.f003:

Cloud Size Checksum
AWS 18,153,127 ETag 9c2353fdc66b9acfdf2a8b46728358d7
Azure 18,153,127 Content-MD5 nCNT/cZrms/fKotGcoNY1w==
GCS 18,153,127 md5Hash nCNT/cZrms/fKotGcoNY1w==

All three serve anonymous HTTP 206 byte-range requests with GRIB magic at byte 0.

Choose on: AWS for the full 2017-onward archive or SNS notifications; GCS for a clean GEFSv12-only archive, provided you don't need wave-product indexes; Azure for the last ~90 days, where it is the most complete mirror.

Byte-range retrieval matters more here than almost anywhere else in the catalog. A single pgrb2b step file is ~98 MB with 505 records, and a full 00 UTC cycle across all 31 members is 549 GB for that product alone. Pulling one parameter across all members via the .idx offsets is the difference between megabytes and hundreds of gigabytes.

Notes

  • GEFS uses the same FV3 dynamical core and physics suite as GFSv15, but at coarser resolution (C384 vs C768) and with stochastic physics added. The 64-level vertical structure is also coarser than the deterministic GFS's 127 levels.
  • The 35-day forecast range at 00 UTC was a major v12 enhancement, motivated by NOAA's growing emphasis on sub-seasonal-to-seasonal (S2S) prediction. The other three cycles remain at 16 days because the additional sub-seasonal members are computationally expensive. Verified: at 00 UTC all 33 prefixes run to 840 h — the extension is not restricted to a member subset.
  • GEFSv12 was the first global-scale coupled forecast system at NCEP under the Unified Forecast System (UFS) framework, deployed in September 2020 — predating the FV3 transition for the deterministic GFS by about nine months (GFSv16 transitioned in March 2021).
  • pgrb2b has no mean or spread. Only pgrb2a and pgrb2s carry geavg/gespr. Users needing ensemble statistics for the extended pgrb2b parameter set must compute them from the 31 members themselves.
  • Grid and length are coupled to product choice, not freely selectable. There is no 0.25° full-field product and no 0.5° product limited to 240 h. The three atmospheric products are three fixed (grid, field-set, length) combinations.
  • Version boundary in the archive. The AWS bucket spans GEFSv11 (2017-01-01 → 2020-09-22) and GEFSv12 (2020-09-23 onward) with different resolutions, member configurations, and directory layouts. Anything crossing that boundary must handle both. GCS sidesteps this by starting after the transition.

Recent version history

GEFSv12 — operational 23 September 2020 (current)

  • Transition to the FV3 dynamical core under the UFS framework — the first global-scale UFS-based system at NCEP
  • Ensemble size increased to 31 members
  • Horizontal resolution increased to C384 (~25 km); 64 vertical levels
  • Forecast range extended to 35 days at the 00 UTC cycle for sub-seasonal guidance
  • Wave ensemble unified into GEFS as a one-way-coupled WW3 component, retiring the standalone Global Wave Ensemble System (GWES)
  • GEFS-Aerosols introduced as a separate GOCART-coupled run
  • Accompanied by the 30-year GEFSv12 reforecast dataset

Upcoming — GEFSv13

Under development for joint deployment with GFSv17 (proposed for October 2026). As with GFSv17, no formal Service Change Notice has been issued; product paths and the product set may change, and this entry's inventory should be re-verified if that upgrade goes operational.

Official documentation