NOUS41 KWBC 211441
PNSWSH
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 Center’s (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 day’s 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
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@noaa.gov
NWS National Technical Implementation
Notices are online at:
http://www.weather.gov/os/notif.htm
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