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					Site-Specific Scanning Strategies for
WSR-88Ds: Planning for Field Tests

                                       Rodger A. Brown
                             NOAA, National Severe Storms Laboratory

                                     Randy M. Steadham
                             NOAA, WSR-88D Radar Operations Center

   National Weather Association Annual Meeting, Cleveland, Ohio, 15-19 October 2006
• The National Weather Service – which has a
  critical need to provide hazardous weather
  warnings to the public – is served by radars that
  currently have inadequate scanning strategies
• When WSR-88D radars were installed in the
  early 1990s, the lowest elevation angle was set
  at 0.5o – even though mountaintop radars would
  overshoot crucial low-altitude phenomena
         Forecaster Requests
Soon after the WSR-88Ds were installed, the
following types of requests were being made:
• Extend the lower limit of elevation angles to as much
  as -1.0o for mountaintop WSR-88D sites in the Western
  Region of the National Weather Service (1995)
• Decrease the lowest elevation angle to 0.2o for WSR-
  88Ds in the Great Lakes region in order to monitor
  shallow lake-effect snowstorms (1995)
2006 Survey of NWS Offices
                • A decade later, there
                  still is a need for lower
                  elevation angles
                • One sixth of the
                  responses to a recent
                  survey indicate the
                  need for elevation
                  angles below 0.5o
How Low Can A WSR-88D Scan?
• Based on a theoretical study by Paul Smith
  (1998 J. Atmos. Oceanic Technol.), the lowest
  reasonable elevation angle is 0.25 – 0.35
  beamwidths above the ground
• For a WSR-88D, this means that the lowest
  elevation angle can be within 0.2o – 0.3o of the
• WSR-88Ds can physically scan as low as –1.0o
     Simulations - Cedar City, UT

With negative elevation angles, KICX in southwestern Utah can
make much more accurate estimates of precipitation rates
     Simulations - Montague, NY

KTYX, overlooking Lake Ontario and surrounding terrain, can
better detect shallow lake-effect snowstorms (dashed line) and
better estimate snowfall rates with lower elevation angles
        Benefits of Lower Angles
• Better estimates of surface rainfall and snowfall rates
• Better detection of outflow boundaries that can
  represent damaging winds
• Better detection of surface boundaries that can
  initiate convective storms and “gustnadoes”
• Better detection and monitoring of tornadoes
• Better detection of damaging microbursts
• Better detection and tracking of shallow storms
• Better monitoring of distant storms
         SSSS Working Group
• In 2005, the WSR-88D Radar Operations Center
  (ROC) established a Site-Specific Scanning
  Strategy (SSSS) Working Group
• The goal of the SSSS Working Group is to
  investigate the benefits of lowered elevation
  angles by conducting field tests at a few WSR-
  88D sites
        SSSS Working Group
• Working Group members come from the ROC,
  National Severe Storms Laboratory, the involved
  NWS Forecast Offices, NWS Warning Decision
  Training Branch, NWS Headquarters, FAA, U.S.
  Air Force, and South Dakota School of Mines &
WSR-88D Sites
            • Mountaintop
              radars in red
            • Also note the
              number of radars
              surrounding the
              Great Lakes and
              along both coasts
               Field Test Plan
• The plan is to conduct a two-year field test at
  three WSR-88D sites on the tops of mountains
  and three sites on relatively flat terrain, with lower
  elevation angles tailored for each specific site
• The lower elevation angles would be appended to
  the current scanning strategies, but they would
  not affect the current processing and distribution
  of radar data
             Field Test Plan
• Instead, there would be a second Radar Product
  Generator (RPG) at each site (with a separate
  ID) to process and distribute data from the lower
  angles as well as from the regular elevation
• The test data would be available to the local
  forecast office and to Working Group members
  via the regular WSR-88D distribution network
            Field Test Status
• Being a new project, the test plan is making its
  way through the NWS’s Operations and
  Services Improvement Process (OSIP)
• The OSIP process has a number of unknowns,
  so we are in a wait–and–see mode
• To take full advantage of the detection and
  warning potential of WSR-88Ds, the lowest
  elevation angle should be within 0.2o– 0.3o of
  the terrain
• A field experiment is being pursued that will
  test the benefits of lowering the elevation
Rodger.Brown@noaa.gov   Randy.M.Steadham@noaa.gov

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