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  • NCDC Radar Resources

    Welcome to the NCDC Radar Page

    Please hover your mouse over the links to the upper left, or simply scroll down the page to select and view more content from this area of the NCDC website. This is the first in a series of steps we're taking to improve our site. Should you have something specific to look for, submit a search in the golden search bar above.

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    Go to top of page Latest News

    Dual-Polarization NEXRAD Level-II and Level-III products - Technical Information Notice
    Higher Resolution for NEXRAD Level-III products - Technical Information Notice
    FAA Terminal Doppler Weather Radar Level-III products - Technical Information Notice
    Level-III Clutter Filter Product Code Change - Technical Information Notice
    01/15/2009 U.S. Airways New York City Accident
    Weather and Climate Toolkit
    Level-II Format Change - Technical Information Notice
    Level-II Format Change - Notification
    Dual-Polarization Sample Data!
    Korean Data Available

    Click on to access the RSS Feed. ( What is RSS? )

    Go to top of page Welcome

    Top of Page Introduction

    Radar data and derived products are available at no cost through the National Climatic Data Center. The system from which these data are collected is the Weather Surveillance Radar-1988 Doppler network (WSR-88D Radar) which began operation at a few sites in 1991.

    Top of Page What is NEXRAD?

    The Next Generation Weather Radar system (NEXRAD) comprises 159 Weather Surveillance Radar-1988 Doppler (WSR-88D) sites throughout the United States and select overseas locations. This system is a joint effort of the United States Departments of Commerce (DOC), Defense (DOD), and Transportation (DOT). The controlling agencies are the National Weather Service (NWS), Air Force Weather Agency (AFWA) and Federal Aviation Administration (FAA), respectively. Level II data are the three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width. From these quantities, computer processing generates numerous meteorological analysis products known as Level III data. Level II data are recorded at all NWS and several select CONUS DOD WSR-88D sites. Level III products are recorded at 155 of the 159 sites. The data are sent to the National Climatic Data Center (NCDC) for archiving and dissemination.

    See the NEXRAD Inventory or the NEXRAD Product List for additional information.

    Detailed information can be found at the NEXRAD Radar Operations Center

    Top of Page How does the radar collect data?

    Three functional components make up the WSR-88D: Radar Data Acquisition (RDA), Radar Product Generator (RPG), and the Open Principal User Processor (OPUP). To adequately sample the atmosphere, the WSR-88D employs nine scanning strategies or volume coverage patterns (VCPs). A VCP is a series of 360 degree sweeps of the antenna at pre-determined elevation angles completed in a specified period of time. Other scan strategies maybe implemented in the future.

    Volume Coverage Pattern 121: This VCP implements the multi-pulse repetition frequency detection algorithm (MPDA) which helps mitigate range/velocity aliasing (the Doppler Dilemma). This VCP has the same elevation angles (9) as VCP 21, but completes 20 azimuthal scans in 5 minutes.

    Volume Coverage Pattern 12: This VCP has the same number of elevation angles as VCP 11. However, denser vertical sampling at lower elevation angles provides better vertical definition of storms, improves the detection capability of radars impacted by terrain blockage for better rainfall and snowfall estimates, results in more storms being identified, and provides quicker updates. This VCP has 14 elevation angles and completes 17 azimuthal scans in about 4.5 minutes.

    Volume Coverage Patterns 11 and 21: These VCPs are used in the Precipitation Mode to better sample the vertical structure of convective weather echoes and to provide better temporal resolution. VCP 11 provides better vertical sampling of weather echoes than VCP 21 and is usually preferred in situations where convective precipitation is within 60 nmi of the antenna. The VCP 11 has 14 elevation angles and completes 16 azimuthal scans in 5 minutes while VCP 21 has 9 elevation angles and completes 11 azimuthal scans in 6 minutes.

    Volume Coverage Patterns 31 and 32: Both of these VCPs are used in the Clear-Air Mode to optimize the sensitivity of the WSR-88D. The VCP 31 (long pulse) provides a better signal-to-noise ratio permitting lower reflectivity returns to be detected, while VCP 32 (short pulse) provides a higher unambiguous velocity. Both VCPs have 5 elevation angles, 7 azimuthal scans, and take 10 minutes to complete.

    Volume Coverage Patterns 211, 212, and 221: These VCPs have the same elevation angles as VCPs 11, 12, and 21 respectively. These VCPs implement the Sachidananda-Zrnic Algorithm (SZ-2) which is applied on the "split cuts" (generally elevation angles below 1.5° except for VCP 31 which has a split cut at 2.5°). See Chapter 5, Part C, of the Federal Meteorological Handbook No.11 (FMH-11) for additional information on split cuts. The SZ-2 Algorithm reduces range ambiguity for Doppler data.

    For more information on radar data visit the NEXRAD Radar Operations Center.

    Top of Page Where can I get details on NEXRAD radar?

    Details on the NEXRAD RADAR system are available in Federal Meteorological Handbook No. 11 (FMH-11). The handbook consists of four volumes and covers RADAR concepts, theory, products and analysis. The handbooks are available for download from the Office of the Federal Coordinator for Meteorology (OFCM)

    The four FMH-11 volumes are:

    A - System Concepts, Responsibilities, and Procedures.
    B - Doppler Radar Theory and Meteorology.
    C - Products and Algorithms.
    D - Unit Description and Operational Analysis.


    A considerable amount of free information on the NEXRAD Radar System can be obtained through the NCDC web pages:

    Top of Page What is the cost of NEXRAD data?

    Digital Radar Data may be downloaded at no cost from NCDC. ( Download Radar Data )

    Hardcopy Radar Maps may also be ordered for a small fee. ( Order Radar Hardcopy )

    Top of Page Top of Page