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Service Change Notification 25-32 Updated
National Weather Service Headquarters Silver Spring MD
1130 AM EDT Thu May 22 2025

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

From: Patrick T. Marsh
 Chief, Science and Support
 NWS/Storm Prediction Center

Subject: UPDATED: Upgrade to SPC post processing for NCEP
models, Effective May 27, 2025

Updated to Remove/Correct invalid links.

On or about May 27, 2025, beginning with the 1200 Universal
Coordinated Time (UTC) model run, the National Centers for
Environmental Prediction (NCEP) will upgrade SPC_POST, SPCs
postprocessing package for the NCEP model suite, to v2.1.

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.

Changes with this upgrade include:
The output of GEFS-MLP was changed to be more consistent with
the other calibrated guidance in SPC_POST.  Previously, the data
in the GEFS-MLP files were given as a fractional probability
between 0 and 1.  However, with this update, the output is
changed to be a percentage between 0 and 100.

In order to facilitate dry thunderstorm forecasting, SPC_POST
v2.1 adds calibrated lightning density guidance from the HREF.
This guidance uses machine learning and outputs the probability
of 25, 50, 100, and 200 cloud-to-ground lightning flashes over a
4-hour period.The naming convention for these files is

ltgdensity/spc_post.tCCz.hrefld_4hr.fFFF.grib2

where CC is the HREF cycle (00 or 12) and FFF is the 3-digit
forecast hour.These files will be available at:

https://nomads.ncep.noaa.gov/pub/data/nccf/com/spc_post/prod/
ftp://ftpprd.ncep.noaa.gov/data/nccf/com/spc_post/prod/

NCEP urges all users to ensure their decoders can handle changes
in content order and volume changes.  These elements may change
with future NCEP model implementations.  NCEP will make every
attempt to alert users to these changes before implementation.
As part of NCEPs standard 30-day parallel testing, the new
output products will be available here:

https://nomads.ncep.noaa.gov/pub/data/nccf/com/spc_post/para/
ftp://ftpprd.ncep.noaa.gov/data/nccf/com/spc_post/para/

For questions regarding this change, please contact:

Tim Supinie
NWS/Storm Prediction Center, Norman, OK
tim.supinie@noaa.gov

For questions regarding the data flow, please contact:
Margaret Curtis
NCEP Central Operations HPC Dataflow Team Lead
Email: ncep.pmb.dataflow@noaa.gov

National Service Change Notices are online at:

http://www.weather.gov/notification/