NOAA GFS levels: PV, AGL and special surfaces

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What the complete inventory covers

Checked actual NOAA NOMADS indexes for GFS 0.25°, 13 October 2026, 00 UTC run, f003 (+3 hours, valid 03 UTC). The main pgrb2 file has 743 records and 98 distinct level labels; supplementary pgrb2b has 349 records and 43 labels. Their union contains 130 unique labels.

A separate table lists all 129 named entries in NOAA/NCEP GRIB2 Code Table 4.5, revision 11 June 2026. This wider classification also covers ocean, soil, ice and other products.

Download the complete snapshot: levels, parameters, sources and codes (JSON)

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PV: potential-vorticity surfaces

Potential vorticity combines air rotation and stratification. A PV surface is defined by a specified value of this quantity, not by pressure, wind speed or geometric height.

The main GFS file has +2 and −2 PVU surfaces. The supplementary file adds ±0.5, ±1 and ±1.5 PVU. PV=2e-06 (Km^2/kg/s) surface means +2 PVU: K denotes kelvin and m² square metres, not square kilometres.

Surfaces near 2 PVU are used in dynamic-tropopause and stratospheric-intrusion analysis. They need not coincide with a separately diagnosed tropopause surface. Preserve the sign; positive and negative values are not interchangeable magnitudes.

1 PVU = 10⁻⁶ K·m²·kg⁻¹·s⁻¹

PV=5e-07 → +0.5 PVU; PV=-1.5e-06 → −1.5 PVU

NOAA CPC: 2 PVU height and stratospheric intrusions

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AGL-PH: pressure relative to the ground

Labels such as AGL-PH, AGL pressure or hPaAGL usually refer to pressure differences relative to the surface. NOAA inventory uses “mb above ground”; the GRIB2 type is 108. AGL-PH is not a separate official NOAA type name: check the metadata behind any application-specific abbreviation.

At surface pressure pₛ, a pressure deficit Δp defines p = pₛ − Δp. A larger deficit is the higher boundary. With pₛ = 1000 hPa, 90–60 mb above ground has lower and upper boundaries of 940 and 910 hPa.

With pₛ = 850 hPa the same layer runs from 790 to 760 hPa. It is neither fixed metres AGL nor a fixed isobaric surface.

p = pₛ − Δp; 1 mb = 1 hPa = 100 Pa

90–60 mb above ground: lower deficit = 60 hPa; upper deficit = 90 hPa

Diagram: pressure layers above local ground

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Sigma and hybrid: model coordinates

Sigma is a dimensionless pressure coordinate normalized to the surface. In the simple σ = p / pₛ system, σ = 0.995 gives approximately 995 hPa at pₛ = 1000 hPa, but 796 hPa at pₛ = 800 hPa. A system with nonzero top pressure may use σ = (p − pₜ) / (pₛ − pₜ); follow the product definition.

A hybrid system combines terrain-following behaviour below with another coordinate aloft. “1 hybrid level” is a model-level index, not 1 m or 1 hPa. Locating it requires coefficients and model state.

Hybrid pressure: p(k) = A(k) + B(k) × pₛ

Hybrid height: z(k) = A(k) + B(k) × orog

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Special surfaces, layers and the atmospheric column

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Every numeric GFS level and layer boundary

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Other NOAA types absent from these files

GRIB2 defines types not present in the checked GFS pair. They serve other output products, diagnostics, models and physical environments. Do not automatically treat them as available map layers.

NOAA CPC: potential temperature and isentropic surfaces

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Complete inventory: 130 GFS labels

Exact inventory labels are preserved for matching against NOAA .idx files. Every row identifies the files and all parameters found at that level. A label occurs once even when present in both files.

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Complete classification: 129 GRIB2 types

All named entries in NOAA/NCEP Code Table 4.5 are listed, including NCEP local extensions. Official English names preserve lookup compatibility. The unit belongs to the surface coordinate or threshold, not the weather parameter. A dash means the table specifies no unit for that type.

Reserved codes and ranges are not level types. Code 255 means missing. Codes 192–254 are local-use values: do not apply NCEP definitions to another producer without checking. Refer to the original table for its explanatory notes.

Original NOAA table 4.5 with all notes

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Choosing a level for your task

1. For near-surface wind, look for 10 m above ground; for air temperature, 2 m above ground. SFC has a different meaning.
2. For a flight level, obtain standard pressure first, then use profile fields and HGT as described in the altitude article.
3. Distinguish diagnosed tropopause from a PV surface, and metres AGL from pressure deficit above ground.
4. Check that the parameter exists at the level. For example, 4000 m above ground in this snapshot contains REFD, not TMP.
5. Preserve type, both layer boundaries, units, parameter, valid time and source. Numbers such as 2, 0.995 and 90–60 are ambiguous without the level type.

Check your understanding

Answer first, then expand the question.

NOAA sources and verification scope

GFS levels were extracted from actual .idx files; types were extracted from NOAA/NCEP Code Table 4.5. Static product pages were used to interpret fields. The saved JSON includes source URLs, record counts and SHA-256 hashes of the indexes.

• NOAA/NCEP: GFS pgrb2 inventory — parameters and levels in the main GFS 0.25° f003 file
• NOAA/NCEP: GFS pgrb2b inventory — additional parameters and levels
• NOAA/NCEP: GRIB2 Code Table 4.5 — official surface and layer types
• NOAA NOMADS: GFS 0.25° pgrb2 f003, 2026-10-13 00 UTC — checked main index; NOMADS retains it for a limited time
• NOAA NOMADS: GFS 0.25° pgrb2b f003, 2026-10-13 00 UTC — checked supplementary index; a local snapshot is preserved
• NOAA CPC: Stratospheric Intrusion Monitoring — use of the 2 PVU surface
• NOAA CPC: Isentropic Analysis Information — potential temperature and isentropic surfaces

Checked 13 October 2026. GFS snapshot: 00 UTC, f003. Classification revision: 11 June 2026.