NOUS41 KWBC 261858 AAA



Technical Implementation Notice 13-25, Amended

National Weather Service Headquarters Washington DC

200 PM EDT Fri Sept xx 2013


To:       Subscribers:

          -Family of Services

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          -Other NWS Partners, Users and Employees


From:     Tim McClung

          Science Plans Branch Chief

          Office of Science and Technology


Subject:  Amended: Change to Great Lakes Wave Model Physics:    

          Effective October 22, 2013


Amended to change implementation date from October 1, 2013, to

October 22, 2013, to allow for additional testing and evaluation


On or about October 22, 2013, beginning with the 1200 Coordinated

Universal Time (UTC) cycle, the National Centers for

Environmental Prediction (NCEP) will introduce a physics upgrade

to the Great Lakes Wave Model, which will affect both the early

and late model runs GLW and GLWN.


The key changes for the Great Lakes system are as follows: a new

physics package for wave growth under wind seas and for wave

dissipation due to wave breaking.  The new physics packages are

outlined in Ardhuin et al. 2010. A validation study made using

NCEP's Great Lakes wave models is presented in Alves et al., 2013

(see full reference below). The latter work shows that the new

physics significantly improves model skill for wave height,

especially in regions of strong storm wind forcing. This will be

reflected by crucial improvements in forecast performance for

extreme wave prediction, a systematic problem in previous

GLW/GLWN systems. Correction will boost usage of the system by

Great Lakes WFOs.  All output products will remain unchanged.


With this implementation, the location of the output data on the

ftp servers will be changed. Data are currently available in a

general directory named "wave."  With this implementation, the

GLW and GLWN will be put in a directory named "glw."  The full

directory paths are listed below.


The output data from these models will be disseminated on the

NCEP server at



and on NOMADS at


where YYYYMMDD is the 4-digit year, month and day.  Note that

prior to the implementation the data are available in



Sample output files from the new physics are available at


Details about the NCEP Multi-grid Wave Model are online at:


A consistent parallel feed of data will be available on the NCEP

server once the model is running in parallel on the NCEP Central

Computing System in early September. The parallel data will be

available via the following URLs:


NCEP urges all users to ensure their decoders can handle changes

in content order, changes in the scaling factor component within

the product definition section (PDS) of the GRIB files, changes

to the GRIB Bit Map Section (BMS), and volume changes. These

elements may change with future NCEP model implementations. NCEP

will make every attempt to alert users to these changes before



For questions regarding these model changes, please contact:


Hendrik Tolman

NCEP/Marine Modeling and Analysis Branch

Camp Springs, Maryland

301-763-8000 ext 7253


For questions regarding the dataflow aspects of these data sets,

please contact:


Rebecca Cosgrove

NCEP/NCO Dataflow Team

Camp Springs, Maryland 20746

301-763-8000 x 7198




Alves et al., 2013: The Operational Implementation of a Great

Lakes Wave Forecasting System at NOAA/NCEP. Weather and

Forecasting, early online release:


Ardhuin, F. et. al., 2010: Semi-empirical dissipation source

functions for ocean waves: Part 1, definition, calibration and

validation. J. Phys. Oceanogr., 40, 1917-1941.


NWS technical implementation notices are online at: