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NOUS41 KWBC 281605

Technical Implementation Notice 14-52
National Weather Service Headquarters Washington DC
1105 AM EST Wed Jan 28 2015

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:  Corrected: Changes to the Great Lakes Wave (GLW)
          System Effective January 28, 2015

Corrected an error for the new 2.5km file names which should be:

Also, the implementation date changed from January 27, 2015, to
January 28, 2015, because of a critical weather day.

Effective Wednesday, January 28, 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

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 smartinit
-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.grlc_2p5km.tCCz.grib2 - NAM smartinit forcing
glwn.grlc_2p5km.tCCz.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:

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