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NOUS41 KWBC 182115
PNSWSH

Service Change Notice 25-80
National Weather Service Headquarters Silver Spring MD
415 PM EDT Tue Nov 18 2025

To: Subscribers:
 -NOAA Weather Wire Service
 -Emergency Managers Weather Information Network
 -NOAAPort
 Other NWS Partners, Users and Employees

From: David Michaud
 Director, NCEP Central Operations

Subject: Implementation of the Domestic Aviation Forecast System
(DAFS) v1.0: Effective December 18, 2025

Effective Dec 18, 2025, the National Centers for Environmental
Prediction (NCEP) will implement the Domestic Aviation Forecast
System (DAFS) v1.0.  This new system is an integrated suite of
aviation weather products and will provide a consistent and
comprehensive set of aviation forecasts for the contiguous
United States and Alaskan domain.  This implementation comes as
a result of safety recommendations from the FAA and NTSB.

In the event that the implementation date is declared a Critical
Weather Day (CWD), an Enhanced Caution Event (ECE), or other
significant weather is occurring or is anticipated to occur,
implementation of this change will take place at 1200 UTC on the
next weekday not declared a CWD and when no significant weather
is occurring.

Summary of Changes

(A) The DAFS v1.0 is a new standalone system which utilizes the
Unified Post Processor (UPP) to produce 3 km Inflight Icing
(IFI), also known as Forecast Icing Product (FIP), and Graphical
Turbulence Guidance (GTG) products from the High Resolution
Rapid Refresh (HRRR) model.

Several enhancements to the underlying science will be
implemented for IFI v2.0.  These changes include using explicit
Liquid Water Content in place of Total Water Content (TWC), with
the exception of cloud boundary identification which still uses
TWC, and an assumption that explicit model supercooled rain
implies corresponding Supercooled Large Droplets (SLD).

Similarly, science changes will be made for the GTG v4.0. First,
an improved low-level turbulence diagnostic was incorporated.
Second, the clear air turbulence (CAT) and mountain wave
turbulence (MWT) diagnostics have been updated and expanded.
Third, the GTG will also include an in-cloud, convectively
induced turbulence parameter (CIT). Lastly, diagnostics and
calibrations have been distinguished separately for the
Planetary Boundary Layer (stable or unstable), troposphere and
stratosphere.

(B) IFI v2.0 includes three components: Icing Probability, Icing
Severity and SLD with hourly cycles over the CONUS domain and
three-hourly cycles over the Alaska domain.

3 km IFI v2.0 GRIB2 files will be newly added to the NOAA
Operational Model Archive and Distribution System (NOMADS), for
both the CONUS and Alaska domains, with the following details:
 Both CONUS and Alaska domains
   - 60 levels every 500 ft from FL010 to FL300
   - Icing Severity:
1. GRIB2 CODE TABLE is 4.228
2. GRIB2 parameter number is 37, mnemonic is icesev
   - Background generating process identifier is 0
   - Packing type:
Complex3 packing with bitmap
 CONUS domain
   - Hourly cycles with hourly forecasts from F001-F018
   - File size:
26M/forecast hour, 468M/cycle
 Alaska domain
   - Three-hourly cycles with hourly forecasts from F001-F018
   - File size:
35M/forecast hour, 630M/cycle

13 km IFI v2.0 GRIB2 files for the CONUS domain will be
available over the SBN, to replace the RAP-based 13 km IFI v1.0.
In addition to the GRIB2 changes listed above, SBN specific
changes include:
  - Modification of WMO header site ID from KKCI to KWBA
  - Complex3 packing with no bitmap in place of JPEG2000
packing used by IFI v1.0
  - Hourly forecasts with hourly cycles from F001-F018 in place
of selective hours F01 F02 F03 F06 F09 F12 F15 F18
  - Addition of WMO headers in accordance with additional
forecast hours. Full WMO header details by parameter:
    Icing probability: YAW[B-S]ii KWBA
    Icing severity: YLX[B-S]ii KWBA
    SLD: YAX[B-S]ii KWBA

(C) GTG v4.0 includes five components produced hourly: CAT, MWT,
CIT, 2D maximum on individual flight levels, and a 3D column
max. GTG v4.0 will solely be available over the CONUS domain.

3 km GTG v4.0 GRIB2 files will be available on NOMADS. Changes
from the current RAP based 13 km GTG v3.0 files available on
NOMADS include:
 - CONUS domain
 - Hourly forecasts from F000-F018
 - Addition of new CIT parameter:
    GRIB2 parameter number for the new CIT parameter is 50
 - Change to individual flight level max EDR parameters:
    GRIB2 parameter number for individual level max EDR is 30
    (EDPARM), from the current 31 (MXEDPRM)
 - Change to column max EDR parameter:
      GRIB2 fixed surface type (Code table 4.5) for column max
      EDR is 10 (Entire Atmosphere), from the current 102
      (Specific Altitude Above Mean Sea Level)
 - File size:
      155M/forecast hour, 2.7G/cycle
 - Packing type:
      Complex3 packing with bitmap

13 km GTG v4.0 GRIB2 files will be available over the SBN, to
replace RAP based 13 km GTG v3.0. In addition to the GRIB2
changes listed above, SBN specific changes include:
 - Modification of WMO header site ID from KKCI to KWBA
 - Complex3 packing with no bitmap in place of simple packing
used by GTG v3.0
 - Addition of WMO header for CIT component. Full WMO header
details by parameter:
      CAT: YVW[A-D,G,J,M,P,S]ii KWBA
      MWT: YWN[A-D,G,J,M,P,S]ii KWBA
      CIT: YLW[A-D,G,J,M,P,S]ii KWBA
      Max: ZVW[A-D,G,J,M,P,S]50 KWBA

(D) NOMADS link to access DAFS GRIB2 files containing non-WMO
headed products during the 30-day parallel:
 - https://nomads.ncep.noaa.gov/pub/data/nccf/com/dafs/para
 - ftp://ftp.ncep.noaa.gov/data/nccf/com/dafs/para

NOMADS link to access DAFS GRIB2 files containing non-WMO headed
products post implementation:
 - https://nomads.ncep.noaa.gov/pub/data/nccf/com/dafs/prod
 - ftp://ftp.ncep.noaa.gov/data/nccf/com/dafs/prod

Filenames during the 30-day parallel and post-implementation
will have the patterns:
 - GTG: dafs.tHHz.gtg.3km.conus.fCCC.grib2
 - IFI-CONUS: dafs.tHHz.ifi.3km.conus.fCCC.grib2
 - IFI-AK: dafs.tHHz.ifi.3km.ak.fCCC.grib2

(E) Previous 13 km RAP versions of GTG and IFI will be removed
from the NWS TGFTP upon DAFS implementation. Users are
encouraged to transition to the new GTG v4.0 and IFI v2.0 GRIB2
files available on NOMADS.
 - GTG to be removed:
https://tgftp.nws.noaa.gov/SL.us008001/DC.avspt/DS.gtggb/PT.grid
_DF.gr2/ with filename pattern: sn.*.bin
 - IFI to be removed:
https://tgftp.nws.noaa.gov/SL.us008001/DC.avspt/DS.fipgb/PT.grid
_DF.gr1/ with filename pattern: sn.*.bin

NCEP encourages users to ensure their decoders are flexible and
are able to adequately handle changes in content order, changes
in the scaling factor component within the product definition
section (PDS) of the Gridded Binary (GRIB) files, and any volume
changes which may be forthcoming. These elements may change with
future NCEP model implementations. NCEP will make every attempt
to alert users to these changes prior to any implementations.

For more information on DAFS icing and turbulence parameters,
please see the following links to their respective product
description documents:
GTG4:
https://nsdesk.servicenowservices.com/api/g_noa/nwspc/res2/62bbb
ccb47f8f290f6550c03e16d4351

IFI2:
https://nsdesk.servicenowservices.com/api/g_noa/nwspc/res2/dc3cf
44f47f8f290f6550c03e16d43d0

Please submit comments, questions, or requests pertaining to
this upgrade to:

Dr. Joshua Scheck
Chief, Aviation Support Branch
Aviation Weather Center
joshua.scheck@noaa.gov

For questions about the dataflow aspects, please contact:

Margaret Curtis
NCEP Central Operations HPC Dataflow Team Lead
ncep.pmb.dataflow@noaa.gov

National Service Change Notices are online at:

https://www.weather.gov/notification/