NOUS41 KWBC 111218



Technical Implementation Notice 16-12

National Weather Service Headquarters Washington DC

118 PM EDT Thu Apr 14 2016


To:         Subscribers

            -NOAA Weather Wire Service

            -Emergency Managers Weather Information Network


            Other NWS Partners and Employees


From:       Stephen Del Greco

            Program Manager, NEXRAD Archive at NOAA’s National

            Centers for Environmental Information (NCEI)


Subject:    NEXRAD Level-II format at NCEI Archive Changes

            Scheduled To Begin June 1, 2016


NCEI is changing the process and format used to ingest and

archive the NEXRAD Level-II Radar Data beginning June 1, 2016. 

The new data format is now going to preserve the internal

compression used during the transmission of data to NCEI.  This

format is common throughout the Radar community.  A variety of

Radar tools and libraries, listed on the NCEI website, support

the format.  Supported tools:


This change only affects Level-II data after June 1, 2016. 

There will be no change to historical data.


Overview of upcoming changes:


The naming convention for the archived hourly tar files will change.


Current example file name:



New example file name:



The additional "BL" in the product section of the file name

indicates that the volume scan files within the archived tar

files use custom Block BZip2 internal compression.


The naming convention of the volume scan files will also change.


Current example file name:



New example file name:



The .ar2v extension of the file name indicates that the volume

scan files within the tar file use custom Block BZip2 internal



The binary file format:

The internal binary file format will remain "Message 31" as

defined in the Interface Control Documents (ICDs) provided by

the NWS Radar Operations Center (ICD FOR RDA/RPG documents).


The upcoming change pertains to the collection and storage of

data at NCEI. NCEI receives these data in multiple messages,

each representing a portion of a sweep, and then concatenates

the messages to create the entire volume scan. Each message has

an uncompressed header, followed by bzip2-compressed content. 

NCEI is currently decompressing these messages before combining

them into the volume scan file. The volume scan file is

compressed using gzip compression.


After the upcoming change, NCEI will no longer decompress these

messages and will instead concatenate the compressed messages

into the single volume scan file. The volume scan file will not

be recompressed, because the data inside is already received as

bzip2 compressed messages. The Radar Operations Center

documentation describes the transmission method. (ICD for

ARCHIVE II/USER documents)


Sample Data:


Samples of the new data format are available from NCEI.  From

the Archive Access system:


Expand the "Radar menu" and select "NEXRAD Level II - Block

BZip2 Format" (Example data for upcoming archive format change)


For questions or comments, please contact:


      NCEI Customer Service

      NOAA's National Centers for Environmental Information


National Technical Implementation Notices are online at: