NOUS41
KWBC 161933 AAD
PNSWSH
Technical
Implementation Notice 11-54, Amended
National
Weather Service Headquarters Washington DC
330 PM
EDT Mon Apr 16 2012
To: Subscribers:
-Family of Services
-NOAA Weather Wire Service
-Emergency Managers Weather
Information Network
-NOAAPORT
Other NWS Partners, Users and
Employees
From: Tim McClung
Chief, Science Plans Branch
Office of Science and Technology
Subject:
Amended: Change to First Guess Used by Real-Time
Mesoscale Analysis To Rapid Refresh (RAP):
Effective date set for May 1, 2012.
Amended to set the implementation date for Tuesday, May 1,
2012. Users are cautioned that if a Critical
Weather Day (CWD) designation is in effect on May 1, this implementation will
be delayed until the conclusion of CWD. You can monitor the CWD status at the following webpage:
http://www.nco.ncep.noaa.gov/pmb/cwd/
On Tuesday,
May 1, 2012, with the 1200 Coordinated
Universal
Time (UTC) run, the Real-Time Mesoscale Analysis
(RTMA)
for CONUS at both 5-km and 2.5-km resolution will use the Rapid Refresh (RAP) instead of the Rapid
Update Cycle (RUC) as the forecast model
that provides the first guess. The
current
5- and
2.5-km resolution RTMA terrain fields, which were created at ESRL/GSD, will
also be replaced by terrain fields created at NCEP/EMC.
The
RTMA is a set of gridded surface and near-surface analyses that are created by
combining observations with the first guess, weighted by their error
statistics.
The change
of the first guess is necessary since the RUC is being replaced by the RAP on that same date (see NWS Technical Implementation
Notice 11-53 for details of the RUC to RAP transition). The main impact of this change
will occur in areas of sparse observational data where the RTMA analysis relies
more heavily on the guess field than in areas with greater observational
coverage. While the use of the new RTMA terrain will have little impact on the
overall analysis on scales larger than a few grid lengths, users who might be
using the RTMA terrain to locally adjust the analysis are advised of the need
to use the updated terrain provided in the output files.
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 implementation.
For
questions regarding these changes, please contact:
Manuel Pondeca
NCEP/Mesoscale Modeling Branch
Camp Springs , Maryland
301-763-8000 X7734
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
NWS
National Technical Implementation Notices are online at:
http://www.nws.noaa.gov/os/notif.htm
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