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DAFS v1.0 is operational: HRRR-based icing and turbulence replace legacy RAP products

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hrrr rap nbm

NCEP implemented DAFS v1.0 on March 30, 2026, adding 3 km HRRR-based IFI v2.0 and GTG v4.0 aviation products on NOMADS while retiring older RAP-based files.

NOAA/NCEP implemented the Domestic Aviation Forecast System (DAFS) v1.0 on March 30, 2026. DAFS is a new standalone aviation system that uses the Unified Post Processor (UPP) to produce 3 km in-flight icing and graphical turbulence guidance from the High Resolution Rapid Refresh (HRRR) model.

The short version: aviation icing and turbulence guidance moved from older RAP-based 13 km products toward HRRR-based 3 km products, with new GRIB2 files on NOMADS and several legacy files removed.

What DAFS produces

DAFS v1.0 has two main operational product families.

IFI v2.0 covers in-flight icing:

  • icing probability
  • icing severity
  • supercooled large droplets (SLD)

The new 3 km IFI v2.0 GRIB2 files are available for CONUS and Alaska. Both domains use 60 flight levels, every 500 ft from FL010 to FL300. CONUS runs hourly with forecasts from F001-F018. Alaska runs every three hours, also with hourly forecasts from F001-F018.

GTG v4.0 covers turbulence:

  • clear-air turbulence (CAT)
  • mountain-wave turbulence (MWT)
  • convectively induced turbulence (CIT)
  • 2D maximum turbulence on individual flight levels
  • 3D column maximum turbulence

The new 3 km GTG v4.0 GRIB2 files are available for CONUS with hourly forecasts from F000-F018.

Important science and GRIB2 changes

NOAA calls out several changes that matter for decoders and downstream workflows.

For IFI v2.0:

  • explicit Liquid Water Content replaces Total Water Content for the core icing calculation, except for cloud-boundary identification
  • explicit model supercooled rain is treated as implying corresponding SLD
  • icing severity uses GRIB2 code table 4.228, parameter number 37, mnemonic icesev
  • packing is Complex3 with bitmap for the 3 km NOMADS files

For GTG v4.0:

  • low-level turbulence diagnostics were improved
  • CAT and MWT diagnostics were updated and expanded
  • CIT is now included
  • individual-flight-level max EDR changes to GRIB2 parameter 30 (EDPARM)
  • column max EDR uses fixed surface type 10 (Entire Atmosphere)
  • packing is Complex3 with bitmap for the 3 km NOMADS files

NCEP also warns users to keep GRIB decoders flexible for future changes in content order, PDS scaling-factor components, and product volume.

NOMADS paths and filenames

The post-implementation NOMADS path for non-WMO-headed DAFS GRIB2 products is:

https://nomads.ncep.noaa.gov/pub/data/nccf/com/dafs/prod

NOAA lists these filename patterns:

dafs.tHHz.gtg.3km.conus.fCCC.grib2
dafs.tHHz.ifi.3km.conus.fCCC.grib2
dafs.tHHz.ifi.3km.ak.fCCC.grib2

What was removed

When DAFS went operational, NCEP removed the previous 13 km RAP-based GTG and IFI files from NWS TGFTP.

Removed GTG path:

https://tgftp.nws.noaa.gov/SL.us008001/DC.avspt/DS.gtggb/PT.grid_DF.gr2/

Removed IFI path:

https://tgftp.nws.noaa.gov/SL.us008001/DC.avspt/DS.fipgb/PT.grid_DF.gr1/

This also connects to an earlier NBM change. NOAA's NBM notice says the older AWC IFI product was hosted inside NBM core blend files on NOMADS and AWS, but the new DAFS IFI product is not planned to be hosted by NBM because of domain-coverage differences.

If you were getting aviation icing from NBM, the replacement path is DAFS, not a new NBM field.

What this means for GribStream users

GribStream supports HRRR, RAP, and NBM, but DAFS is a separate NOAA aviation product family. The NWS notice gives NOMADS paths for DAFS; it does not announce an AWS Open Data mirror.

That distinction matters. DAFS is derived from HRRR, but it is not automatically part of the core HRRR feed.

It still matters for GribStream users indirectly:

  • the new aviation products are HRRR-derived, so they are downstream of a model GribStream already serves
  • the older IFI product was present in NBM core blend files on NOMADS and AWS, but NOAA says the new DAFS IFI is not planned to be hosted by NBM
  • the legacy products being replaced were RAP-based, so this is also a RAP-to-HRRR transition for aviation icing and turbulence workflows

Because the DAFS files listed here are GRIB2, they also fit GribStream's planned direction of mirroring selected NOMADS-only GRIB data when no S3 bucket exists. There is no GribStream support date to announce yet, but DAFS is a strong candidate because it is operational, GRIB2-based, and directly useful for aviation icing and turbulence workflows.

For now, users migrating from older RAP-based GTG/IFI or NBM-hosted IFI should treat March 30, 2026 as the operational break point and validate against the DAFS filenames and GRIB2 metadata above.

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