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| Upgrade Notice |
| The WSR-88D (Doppler Weather Radar0 is being upgrade locally. There is more information below. |
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Upgrade to Dual Polarization Radar |
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The Doppler Weather Radar (WSR-88D) at the National Weather Service in Little Rock (Pulaski County) recently underwent an upgrade to Dual Polarization technology. The upgrade began on August 21st and was completed on the 26th. |
| In the picture: The WSR-88D (Doppler Weather Radar) at the North Little Rock Airport (Pulaski County). |
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If you are not familiar with this technology, here is a quick Question (Q) and Answer (A)...
Q: What is dual polarization technology and how is it better than conventional Doppler radar?
A: Dual polarization technology is the most significant enhancement to the nation's weather radar network since Doppler was installed in the early 1990s. It provides weather forecasters with new information so they can more accurately track, assess, and warn the public of high-impact weather.
Q: How does dual polarization technology work?
A: Conventional Doppler radars send out a horizontal pulse that gives forecasters a one-dimensional picture of whatever is in the air, precipitation or non-precipitation. It can see precipitation, but can't tell the difference between rain, snow, or hail.
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| Dual-pol radar sends and receives both horizontal and vertical pulses, providing a much more informative two-dimensional picture of whatever is out there. This information helps forecasters clearly identify rain, hail, snow or ice pellets, and other flying objects, improving forecasts for all types of weather. |
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| In the picture: With dual-polarization (right), a storm will be sampled more thoroughly with horizontal and vertical pulases of energy from the radar. |
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Q: Does dual polarization technology improve what forecasters understand?
A. This is the greatest benefit that dual polarization radar provides. Forecasters have a clearer understanding of differing weather types (snow vs. rain vs. hail) and non-weather features (smoke from wildfires), both of which impact public safety. A clearer understanding leads to better communication of conditions to NWS Weather Enterprise partners and the public.
Q: Does dual polarization technology improve what forecasters see?
A: Yes. Dual-pol radar provides efficient ways to improve data quality on radar displays. Forecasters now can easily tell the difference between radar echoes that are precipitation and those that are birds, insects, bats or other non-weather objects, allowing them to focus solely on the weather.
Q: Is there information explaining dual polarization technology that is brief and simple to understand?
A: NOAA produced a short video that explains the basic benefits of dual-pol radar for the general public, http://www.youtube.com/watch?v=tX6LH_l3P3Y.
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There will be 14 new radar products available. One of the products is "CC", or Correlation Coefficient. This is used to provide information about the diversity of hydrometeors. A higher value (closest to 1) implies a uniform precipitation sample, and mostly liquid (rain). Lower values could mean more ice (hail) in the sample or non-meteorological targets (i.e. biological scatterers). |
| In the picture: A Correlation Coefficient (CC) product at 754 am CDT on 08/31/2012 (analyzing a heavy rain band in southeast Arkansas associated with the remnants of Hurricane Isaac). High values close to "1" indicate mostly liquid, although embedded lower values might suggest some hail mixed with rain. |
| The Differential Reflectivity (ZDR) product will allow forecasters to analyze precipitation drop sizes. For example, big liquid drops will be larger in the horizontal than the vertical, and will result in inflated ZDR values. Tumbling ice (hail) or snow crystals would have more of a vertical component and lower values. |
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| In the picture: A Differential Reflectivity (ZDR) product at 754 am CDT on 08/31/2012 (analyzing a heavy rain band in southeast Arkansas associated with the remnants of Hurricane Isaac). High values over 2 dB indicate large raindrops. |
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The Specific Differential Phase (KDP) product can be used to find areas of heavy rain. KDP increases as raindrops become larger and more concentrated. When hail becomes mixed with rain, conventional radar tends to overestimate precipitation amounts. KDP is immune to the effects of hail, allowing for a better sense of where excessive rain is occurring (i.e. flash flooding). |
| In the picture: A Specific Differential Phase (KDP) product at 754 am CDT on 08/31/2012 (analyzing a heavy rain band in southeast Arkansas associated with the remnants of Hurricane Isaac). High values over 3 Deg/km indicate a concentrated area of heavy rain. |
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