NOUS41 KWBC 091227



Technical Implementation Notice 14-52

National Weather Service Headquarters Washington DC

727 AM EST Tue Dec 9 2014



To:        Subscribers:

          -Family of Services

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          Other NWS Partners, Users and Employees


From:     Timothy McClung

          Chief, Science Plans Branch

          Office of Science and Technology


Subject:  Changes to the Great Lakes Wave (GLW) System

          Effective January 27, 2015


Effective Tuesday, January 27, 2015, beginning with the 1200

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

Environmental Prediction (NCEP) will upgrade the Great Lakes Wave

forecasting system (GLW), affecting both early and late runs:


Early run: GLW: at 00Z, 06Z, 12Z and 18Z

Late runs: GLWN: at 03Z, 09Z, 15Z and 21Z


Changes include:


-Increased spatial grid resolution to 2.5km using a curvilinear

Lambert conformal grid

-Increased spectral resolution to expand range to 1Hz

-Increased resolution of input wind fields from NAM                                                                                                


-Improved ice concentration analysis

-Switch to latest wave model version, WAVEWATCH III v4.15.1


The implications of the changes are as follows:


1. Increased spatial grid resolution to 2.5km is expected to

bring improvements in the quality of forecasting with higher

resolution grid better resolving coastal features and better

representing wind fetch geometry near shore and during rapidly

changing conditions. To that end, NCEP is using a new bathymetric

database made available by the NOAA Great Lakes Research

Laboratory (GLERL) at a 30 arcsec resolution, in association with

high-resolution coastlines from NOAA Office for Coastal

Management Digital Coast database, to build the new grids.


2. Spectral resolution will be increased to expand the resolved

frequency range internally to 1Hz, matching the GLW spectral

range extent to that of other wave models, allowing later

introduction of more advanced physics packages.


3. Increased resolution of input wind fields from NAM atmospheric

model smartinit files will allow improved resolution of wind

fields from current 12km to the 4km NAM nest data, with expected

impacts to storm wave forecasting and nearshore wave growth.


4. The increased resolution of the input wind fields will delay

the GLW runs by 40 to 50 minutes.


5. Improved ice concentration analysis will result in better

representation of ice coverage during winter months, which will

render the model a more realistic representation of areas in the

lakes basins exposed to waves.


6. Extension of forecast range in the GLWN runs to 147h addresses

Weather Forecast Offices request to fulfil their mission of

providing forecasts up to that range.


7. Upgrade to the latest WAVEWATCH III code follows regular

procedure to bring all wave models towards using the latest

available technology.


Output Product Changes




New output files using the native curvilinear Lambert conformal

wave model grid at 2.5km resolution will replace the existing 4km

resolution files. The new 2.5km resolution files will also have a

new naming convention.


- New 2.5km Datasets


glw.tCCz.grlc_2p5km.grib2 - NAM smartinit forcing

glwn.tCCz.grlc_2p5km.grib2 - NDFD forcing


- Removed Datasets


glw.grl.tCCz.grib2 - 4km wave grid, NAM forcing

glwn.grl.tCCz.grib2 - 4km wave grid, NDFD forcing - 4km wave grid, NAM forcing ice binary

glw.grl.tCCz.restart - 4km wave grid, NAM forcing restart binary

glw.grl.tCCz.wind - 4km wave grid, NAM forcing wind binary - 4km wave grid, NDFD forcing ice binary

glwn.grl.tCCz.restart - 4km wave grid, NDFD forcing restart


glwn.grl.tCCz.wind - 4km wave grid, NDFD forcing wind binary




The existing 4km wave grid GLW/GLWN datasets available via DODS

and Grib Filter will be transitioned to use the 2.5km datasets.




4km wave grid datasets from the late run GLWN will continue to be

disseminated via AWIPS for use by NWS Weather Forecasting Offices

(WFOs). The grids will eventually be replaced in AWIPS by the

2.5km curvilinear wave grid datasets and phased out in a

subsequent GLW system upgrade expected to occur in mid-2015.


Data Availability


The output data from these models are disseminated on the NCEP

server at




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 the NCEP

server 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,

  College Park, Maryland



For questions regarding the dataflow aspects of these data sets,

please contact:


  Justin Cooke

  NCEP/NCO Dataflow Team

  College Park, Maryland 20746



NWS National Technical Implementation Notices are online at: