[nws-changes] 20110421: NAEF- Fwd: ADMIN NOTICE NOUS41 KWBC

• To: nws-changes@xxxxxxxxxxxxxxxx
• Subject: [nws-changes] 20110421: NAEF- Fwd: ADMIN NOTICE NOUS41 KWBC
• From: Linda Miller <lmiller@xxxxxxxxxxxxxxxx>
• Date: Thu, 21 Apr 2011 09:10:25 -0600

-------- Original Message --------

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NOUS41 KWBC 211441
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Technical Implementation Notice 11-15
National Weather Service Headquarters Washington DC
1042 AM EDT Thu Apr 21 2011

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

From:       Tim McClung
            Science Plans Branch Chief
            Office of Science and Technology

Subject:    North American Ensemble Forecast System
            Modification: Effective May 24, 2011

Effective May 24, 2011, beginning with the 1200 Coordinated
Universal Time (UTC) run, the National Centers for Environmental
Prediction (NCEP) will make a modification to the datasets used
in the North American Ensemble Forecast System (NAEFS)
calculations.  The NAEFS output is derived by combining the NCEP
Global Ensemble Forecast System (GEFS) and the Canadian
Meteorological Centers (CMC) GEFS.  At this time, NCEP receives
raw GEFS output from CMC and bias-corrects the dataset locally
before use in NAEFS calculations. With this implementation, NCEP
will receive bias-corrected CMC GEFS data directly from CMC, and
will no longer compute the bias corrections at NCEP.

This will result in a slight difference in the CMC data used in
NAEFS. Both modeling centers use the same bias-correction
algorithm but minor differences arise due to two factors:
First, NCEP and CMC run their bias correction algorithms on
slightly different model grids. Second, NCEP computed the CMC
bias corrections using data up to the previous day, while CMC
calculates the bias correction using data that includes the
current days values. Tests have shown the differences in the
CMC bias-corrected dataset and the NCEP version of CMC bias-
corrected data to be minor.

There will be no changes in the content of NAEFS products with
this implementation.

NCEP encourages all users to ensure their decoders are flexible
and are able to adequately handle changes in content order,
changes in the scaling factor component within the product
definition section (PDS) of the GRIB files, and also any volume
changes which may be forthcoming. These elements may change with
future NCEP model implementations. NCEP will make every attempt
to alert users to these changes prior to any implementations.

For questions regarding these changes, please contact:

  Yuejian Zhu
  NCEP/EMC, Global Climate and Weather Modeling Branch
  Camp Springs, Maryland
  301-763-8000 x 7052
  Yuejian.Zhu@xxxxxxxx

For questions regarding the dataflow aspects of these datasets,
please contact:

  Rebecca Cosgrove
  NCEP/NCO Dataflow Team
  Camp Springs, Maryland 20746
  301-763-8000 x 7198
  ncep.list.pmb-dataflow@xxxxxxxx

NWS National Technical Implementation Notices are online at:

  http://www.weather.gov/os/notif.htm

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