NOUS41 KWBC 151535



Service Change Notice 17-75

National Weather Service Headquarters Silver Spring MD

1135 AM EDT Thu Jun 15 2017


To:        Subscribers:

           -NOAA Weather Wire Service

           -Emergency Managers Weather Information Network


           Other NWS Partners, Users and Employees


From:      Dave Myrick

           NWS Office of Science and Technology Integration


Subject:   Upgrade to the Great Lakes Wave System

           Effective July 25, 2017


Effective on or about July 25, 2017, beginning with the 

1300 Coordinated Universal Time (UTC) run, the National Centers

for Environmental Prediction (NCEP) will make a major upgrade to

the Great Lakes Wave forecasting system (GLW), henceforth 

labeled Great Lakes Wave Unstructured (GLWU).


Upgrade highlights:


  - Change underlying wave code to WAVEWATCH III v5.16.0

  - Replace native grid for all output

  - Output hourly cycles on Web and NOAAPORT

  - Make physics upgrades


The upgrade includes:


1) For all output, replace native wave model curvilinear 

2.5km Lambert Conformal computational grid with unstructured

grid with element sizes ranging from 2.5km offshore, to 250m at

the coast. The new native wave model unstructured computational

grid will provide resolution of wave guidance in the nearshore

zone not possible previously with a 2.5km grid. The new spatial

grid also resolves properly islands and several coastal

features, such as peninsulas, in a way important for defining

wave-climate variations near the coast, unavailable for this set

of products up to this upgrade.


2) Make physics tune up to augment the benefits of higher

nearshore resolution, adding improved skill to the increased

resolution. This combination provides marine forecasters in the

Great Lakes region with augmented confidence and expanded

usability relative to the existing GLW guidance.


3) Add new hourly cycles to help small craft advisory, expanding

the availability of wave guidance to better reflect rapidly-

changing conditions that may be hazardous to small recreation

and/or commercial marine vessels. The new cycles also bring wave

guidance to a schedule consistent with other short-range

products at NCEP, including the HRRR.


For all output, GLW model will add hourly cycles out for a

short-range forecast for 20 cycles, not including 01, 07, 13 and

19 UTC, which will remain long-range forecast output.


4) Add wave-physics tune up for nearshore applications,

including changes to input, dissipation and a multiple discrete

interaction approximation (multiple-DIA) parameterization for

nonlinear wave-wave interactions


5) Make upgrades to the latest public release of WAVEWATCH III

including several bug fixes, and updates to source-functions

that allowed better tuning of the wave model to the requirements

of the new GLW unstructured grid.


6) Include more effective ice concentrations interpolation and

gap-filling algorithms to eliminate exaggerated ice

concentration coverage nearshore, fixing previous land-sea masks



For all output, the cycles 03, 09, 15, and 21 UTC will shift to

cycles at 01, 07, 13, and 19 UTC instead.


Web Output Product Changes


The following changes apply to products available on the

NCEP dissemination sites:



1) The directory structure is changing


Where YYYY is year, MM is Month, DD is day


2) All file names will change the prefix

glwn.* -> glwu.*


3) New output files with this upgrade - To be used experimentally at marine

forecast offices for the development of improved, more accurate

wave guidance products.

  glwu.grlc_2p5km_sr.tCCz.grib2 - 2.5km resolution, short range

forecasts from 00 to 48.

  glwu.grlr_500m.tCCz.grib2 - 500m resolution, short range

forecasts from 00 to 48.



  Where CC is cycle


4) The long-range forecast hours will be extending from 147 to

149 for files like:


  Where CC is cycles 01, 07, 13, and 19 UTC


5) The point output DBLN6 will no longer be available as the

point falls outside the new unstructured grid. This will affect

the following files:






6) Additional point stations will be available, a description of

these additional stations can be found here:


Web Output Product Removals


1) On the NCEP web services, the following legacy 4km files are

being removed as was announced previously.



2) On the NCEP web services, the following files are being

removed with this upgrade as they are no longer supported under

the Great Lakes Wave model system




NOAAPORT/SBN Product Changes


1) On NOAAPORT/SBN, the 4km wave on grid 176 will be removed.

Users can find the output at the higher resolution 2.5km already

available. To view the full list of output WMO headers being

discontinued please click here:


2) New output will be available on hourly cycles for forecast

hours 00-48. This data will be in addition to the already

available 6 hourly cycles. There will not be any new WMO

headers; users will just see hourly cycle output using the

already defined WMO headers for forecast hours 00-48.


3) For the existing 6 hourly cycle output, forecast hours will

be extended from 147 to 149. See the first section above for

details how the 6 hourly cycle output is shifting. Additional

WMO headers will match pattern:



Sample output files from the new physics are available at


Details about the NCEP Wave Models are found online at:


A consistent parallel feed of data is available on NCEP para



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:


  Jose-Henrique Alves

  NCEP/Marine Modeling and Analysis Branch,

  College Park, Maryland



For questions regarding the dataflow aspects of these data sets,

please contact:


  Carissa Klemmer

  NCEP/NCO Dataflow Team Lead

  College Park, Maryland



NWS Service Change Notices are online at: