NOUS41 KWBC 201820 AAE



Technical Implementation Notice 15-32 Amended

National Weather Service Headquarters Washington DC

1034 AM EDT Tue Oct 20 2015


To:       Subscribers:

          -Family of Services

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network


          Other NWS partners and NWS employees


From:     Timothy McClung

          Chief Operating Officer

          NWS Office of Science and Technology Integration


Subject:  Amended: Upgrade the Short Range Ensemble Forecast

          System Effective October 21, 2015


Amended to:

-Change the implementation date from September 29, 2015 to

October 21, 2015 and to expanded the explanation of the 2m

dewpoint cap


The SREF model upgrades include the following:


- The seven Weather Research and Forecast (WRF) Nonhydrostatic

Mesoscale Model (NMM) members will be eliminated.  This

includes the following members: ctl, n1, p1, n2, p2, n3, p3.


- The Nonhydrostatic Multiscale Model on B-Grid (NMMB) model

members will be increased from 7 to 13 members.  The new NMMB

members will be: n4, p4, n5, p5, n6, p6.


- The Advanced Research WRF (WRF-ARW) members will also be

increased from 7 to 13 members. The new ARW members will be

n4, p4, n5, p5, n6, p6.


- Each ensemble member ID will be encoded in the GRIB data for

the 26 individual raw SREF members.


- Cloud ceiling height will change from Above Ground Level

(AGL) to Above Sea Level (ASL) as requested by the aviation

user community. At the same time, a bug has been fixed in the

mode calculation of cloud ceiling. 


- Science changes include more diversity in model initial

conditions (IC), IC perturbations and physics. The vertical

resolution of the model will increase from 35 to 40 vertical



- Several SREF ARW members (p01, n03, n05 and p06 in particular)

occasionally produce dew-point temperature values at the 2m

level (2m Td) that are erroneously high, with some values

exceeding 90F. These spikes in the 2m Td occur in environments

in which actual values are usually near or exceeding 80F. Three

methods to eliminate these errors were tested by the

Environmental Modeling Center (EMC) and the Storm Prediction

Center (SPC). It was decided that simply capping 2m Td values at

28C (82.4F) was the best approach, and this cap has been added

to the SREF code. The cap preserves good domain-averaged

performance (i.e., no impact on the overall performance of 

2m Td) and corrects the spatial structure of the 2m Td field

while taking care of these occasional high value spikes. The

results of the tests were presented at the EMC implementation

briefing to the NCEP director on September 25, 2015, and can be

viewed at the following location (after the actual

implementation date):


The 2m Td is strictly a diagnostic parameter computed in the

model post processor, and these erroneous spikes do not impact

any other forecast parameters. In other words, the issue is only

pertinent to the 2m Td; there is no effect on the boundary layer

or, more specifically, on any model level. The impact of the

spikes on the 2m Td ensemble products, such as mean and

probability is expected to be minimal, since the majority of the

26 members do not have this issue. The newest version of the ARW

model addresses this issue with a new way of computing 2m Td and

will be used in the next SREF upgrade.


- As a uniform measure across all NCEP regional models (see

BUFR Station change TIN 15-30:


There were 138 new stations added in the bufr/sounding output.

See the above mentioned TIN for the detail changes.


- All SREF-based downstream jobs, such as cyclone track, will

not be impacted in their formats and file names but are

calculated based on new 26 members instead of 21 members,

where new members are n4, n5, n6, p4, p5 and p6.


Graphical data is viewable here:


The Environmental Modeling Center (EMC) Mesoscale Modeling

Branch (MMB) has a publicly available website with more

information concerning the SREF modeling system as well as other

NCEP regional modeling systems:


AWIPS product changes:


The total number of ensemble members in this upgrade will

increase from 21 to 26 due to the discontinuation of the NMM

members and the increase of both the NMMB and ARW members

from 7 to 13 members. The increase in ensemble membership

will be reflected in the following AWIPS products:


- For 2-meter Temperature and 3-hourly Precipitation products

on Grid #221 (32 km North American Lambert Conformal Grid),

the GRIB2 Product Definition Template (PDT) will be modified

to identify the individual ensemble members.


- For the Mean, Probability, and Spread products on Grids #212

(40 km Contiguous United States (CONUS) Lambert Conformal

Grid), #216 (45km Alaska Polar Stereographic Grid), and #243

(Eastern North Pacific Grid), the GRIB2 encoding will reflect

the total increase in ensemble members from 21 to 26.


File name changes:


There will be no changes in the file naming convention for the

NMMB files, where the model core in file names is represented

with the string "nmb"; however, the file naming convention

for all ARW files will be modified by replacing the previous

em string with the arw string.


Also, the file naming convention for the mean, probability and

spread cluster files on the NCEP FTP server and NOMADS will

change to lead with "sref" and the model cycle:


[mean|prob|spread].sref.cluster[1-6].fHH.grib2 ->



where CC is the model cycle (03, 09, 15, 21), HH is the 2-

digit forecast hour (00, 03, 06, ..., 81, 84, 87)


Data delivery timing/volume/content changes:


With this upgrade, no changes in delivery time are expected. 

The GRIB2 product definition section (PDS) will be modified to

identify the individual SREF members.  In combination with the

model ID (111=NMMB and 116=ARW), users will be able to

identify each of the unique SREF members as follows: ctl, p1

(+1), n1 (-1), p2 (+2), n2 (-2), ..., p6 (+6), n6 (-6). Due

to the increase in SREF members from 21 to 26 and the addition

of the member ID to each member's GRIB2 file, users can expect

approximately a 10 percent increase in the data volume for each

of the raw individual ensemble member's files.


Output from the SREF is available for North America, the

Contiguous United States, Alaska and Eastern Pacific domains



NOMADS data is available via the following URL:


Output from the SREF is available for the CONUS domain on the

NWS FTP server at the following location:


where CC is the cycle (03, 09, 15, 21) and YYYYMMDD is the

current date.


A consistent parallel feed of data will be made available on

the NCEP HTTP server at the following URL:


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 occur. 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 the scientific content of the modeling

system, please contact:


     Geoff DiMego


     College Park, Maryland 20740

     Phone: 301-683-3764


     Jun Du


     College Park, Maryland 20740

     Phone: 301-763-3704


For questions regarding the dataflow aspects of these data

sets, please contact:


     Justin Cooke

     NCEP/NCO Dataflow Team

     College Park, Maryland 20740

     Phone:  301-683-0567



NWS Technical Implementation Notices are online at: