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Service Change Notice 26-78 Updated
National Weather Service Headquarters Silver Spring MD
215 PM EDT Fri Oct 2 2026

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

From: David Michaud, Director
 NCEP Central Operations
 National Centers for Environmental Prediction

Subject: Updated: Upgrade to HYSPLIT 9.1 to Couple the Rapid
Refresh Forecast System (RRFS) into HYSPLIT and retire the
coupling of the North American Mesoscale Model (NAM) and the High
Resolution Ensemble Forecast (HREF) with HYSPLIT. Effective Nov
3, 2026

Updated to reflect a new implementation date Nov 3, 2026.

On Nov 3, 2026, the HYSPLIT transport and dispersion model
version 9.0 will be upgraded to version 9.1. In case of Critical
Weather Day or declaration of Enhanced Caution status, this
upgrade may be delayed to the next business day. This version
includes the following upgrades:

- Coupling the Rapid Refresh Forecast System (RRFS) into HYSPLIT
- Retiring the coupling of the North American Mesoscale Model
(NAM) with HYSPLIT.
- Retiring the coupling of the High Resolution Ensemble Forecast
(HREF) with HYSPLIT.

This upgrade will increase the data volume for input, output,
post-process fields and products due to the proposed higher
spatial and vertical resolution.

Specifically, ARL-Packed format meteorological input files will
be extended as follows:

- Add RRFS forecasts formatted for HYSPLIT, over multiple
domains including North American (na), Hawaii (hi), Alaska (ak)
,Puerto Rico (pr) and fire weather (firewx):
 - hysplit.tCCz.rrfs.${domain}
Where domain = na, hi, pr, firewx
 - hysplit.tCCz.rrfsfHH.${domain}
Where domain = ak,conus
where HH = forecast hour (00, 06, 12, 18, 24, 30, 36, 42)

- Add RRFS archived formatted for HYSPLIT, over multiple domains
including North American (na), Hawaii (hi), Alaska (ak) and
Puerto Rico (pr):
 - hysplit.tCCz.rrfsa.${domain}
Where domain = na,ak,hi,pr

For all the files listed above,
where CC = 00, 06, 12, 18 Coordinated Universal Time (UTC) cycle

ARL-Packed format meteorological input files will be removed as
follows:

hysplit.tCCz.nama
hysplit.tCCz.namf
hysplit.tCCz.namsa
hysplit.tCCz.namsa.AK
hysplit.tCCz.namsa.HI
hysplit.tCCz.namsf
hysplit.tCCz.namsf.AK
hysplit.tCCz.namsf.FW
hysplit.tCCz.namsf.FW.center.txt
hysplit.tCCz.namsf.HI
hysplit.tCCz.namsfHH.CONUS
where HH = forecast hour (00, 06, 12, 18, 24, 30, 36, 42)

hysplit.tCCz.rens.hiresw.m0M
Where M = ensemble member (1, 2, 3, 4, 5, 6)

hysplit.tCCz.rens.hrrr.m0M
Where M = ensemble member (1, 2)

hysplit.tCCz.rens.nam.m0M
Where M = ensemble member (1, 2)

where CC = 00, 06, 12, 18 Coordinated Universal Time (UTC) cycle

The expected product delay due to using the new RRFS products:

- canned_wfo.YYYYMMDD/$LOC_tCCz.* -~45 - 50 min late

- dustcs.YYYYMMDD/dustcs.t06z.{sfc,pbl}.1hr{.grib2,_227.grib2}
~11 - 15 min late
- dustcs.YYYYMMDD/dustcs.t12z.{sfc,pbl}.1hr{.grib2,_227.grib2}
~45 - 50 min late

NOTE: These changes will only be applicable to CONUS results.
Alaska and Hawaii will continue using CMAQ v4

Current model data is available here:
https://nomads.ncep.noaa.gov/pub/data/nccf/com/hysplit/prod/

An event driven parallel feed of the HYSPLITv9.1 data is
available on the NCEP sites at the following URLs:
https://nomads.ncep.noaa.gov/pub/data/nccf/com/hysplit/para/

Send any comments on the science aspects of this upgrade to:

Fanglin Yang
Chief, NCEP/EMC Physics and Dynamics Division
Fanglin.Yang@noaa.gov

For questions on the dataflow aspects, please contact:

Margaret Curtis NCO Dataflow Team Lead
ncep.pmb.dataflow@noaa.gov

National Service Change Notices are online at:

https://www.weather.gov/notification