NOUS41 KWBC 271115
Public Information Statement, Comment Request
National Weather Service Headquarters Washington, DC
715 AM EDT Thu Sep 27 2012
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From: John Derber
Acting Chief, Global Climate and Weather Modeling
NCEP/Environmental Modeling Center
Subject: Soliciting Public Comments through November 2, 2012,
on the Removal of NCEP’s Legacy Global Data
The National Centers for Environmental Prediction (NCEP) is
proposing to stop producing the legacy Global Data Assimilation
System (GDAS2) and discontinue all associated output products.
This proposal does not affect any output from the current Global
Data Assimilation System (GDAS1). The NWS is seeking comments on
this proposed change through November 2, 2012.
The GDAS2 are legacy products with a horizontal resolution of
triangular truncation T62 (about 208 km on 28 sigma layers).
The current operational GFS runs at a much higher horizontal and
vertical resolution (T574, about 23 km on 64 hybrid sigma-
pressure layers). GDAS2 files were originally created for
downstream applications and customers unable to handle GFS
resolutions greater than 208 km x 28 vertical levels. The GFS
moved beyond T62 in August 1987 when GFS horizontal resolution
went from R40 to T80. Horizontal resolution increased to T126
four years later (March 1991). Vertical resolution increased from
18 layers to 28 layers 2 years after this (August 1993). Since
then there has been a steady increase in GFS horizontal and
vertical resolution. The operational GFS resolution of T574L64
has been in place since July 2010. EMC is currently working on a
GFS resolution increase package for a future implementation.
The near order magnitude reduction in horizontal resolution of
GDAS2 files represents a significant loss of information in the
analysis and forecast fields with respect to GDAS1 files. Not
only do GDAS2 files have less vertical resolution (28 layers),
the vertical coordinate used in GDAS2 files (pure sigma =
terrain following) differs from that used in current operations
(hybrid sigma-pressure = terrain following near surface
transitioning to isobaric surfaces in the upper atmosphere).
Higher resolution GDAS1 products are available for all GDAS2
products and should be used by downstream applications and
customers in lieu of obsolete GDAS2 files.
The obsolete GDAS2 products and the current GDAS1 operational
products are both available at:
where YYYYMMDD is the 4-digit year, 2-digit month and 2-digit
The following files will be removed if the GDAS2 is discontinued.
The replacement GDAS1 files have the same filename, but with
gdas1 as the prefix in place of gdas2. All of these
corresponding GDAS1 files are currently available at the links
gdas2.txxz.bfyy where yy=00,03,06,09
gdas2.txxz.pgrbanl.grib2 and gdas2.txxz.pgrbanl.grib2.idx
gdas2.txxz.pgrbfyy.grib2 where yy=00,03,06,09
gdas2.txxz.pgrbfyy.grib2.idx where yy=00,03,06,09
gdas2.txxz.sfyy where yy=00,03,06,09
gdas2.txxz.sfluxgrbfyy.grib2 where yy=00,03,06,09
gdas2.txxz.sfluxgrbfyy.grib2.idx where yy=00,03,06,09
In the filenames above, xx equals 00, 06, 12, or 18 depending on
the model cycle.
NWS will evaluate all comments to determine whether to proceed
with this change. If approved, a TIN will be issued giving 30
days notice of the implementation date.
Send comments on this proposal to:
NWS/NCEP Environmental Modeling Center
College Park, MD
NWS/NCEP Central Operations
College Park, MD
National Public Information Statements are online at: