NWS La Crosse: Dual Pol Radar Installation Finished

The exciting dual-polarization radar upgrade to the KARX WSR-88D is finished and successfully back online!

This new technology is part of the NWS vision to build a weather-ready nation to better protect lives and livelihoods, and results in 14 new radar products that enables us to continue providing our suite of high quality products and services to the citizens of southeast Minnesota, northeast Iowa, and western Wisconsin.  This new data will help forecasters identify the type of precipitation that is falling, and improve rainfall estimates.

We strongly encourage all users of these new products to complete a series of online training modules developed by the Warning Decision Training Branch (WDTB). Modules are available for non-NWS meteorologists and non-meteorologists.

What is Dual-Pol?

The current doppler radars transmit and receive pulses of radio waves in a horizontal orientation.  As a result, the radar only measures the horizontal dimensions of targets (e.g. cloud and precipitation droplets).  Dual-polarimetric radar transmits and receives pulses in a horizontal and vertical orientation.  Adding in the vertical component will result in better estimates of the size, shape, and variety of sampled targets.  It is expected that this will result in significant improvements in the estimation of precipitation rates, the ability to discriminate between precipitation types (e.g. hail vs. rain), and the identification of non-meteorological returns.

 Current NWS doppler radar
 Dual-pol radar
Current NWS doppler radar Dual-polarimetric radar

Benefits of Dual-Pol
  • Improved accuracy of precipitation estimates, leading to better flash flood detection
  • Ability to discern between heavy rain, hail, snow, and sleet
  • Improved detection of non-meteorological echoes (ground clutter, chaff, anomalous propagation, birds and insects)
  • Identification of the melting layer
  • New severe storm signatures (hail detection, updraft detection, tornadic debris)

Dual-Pol will not improve tornado lead times or be able to provide exact precipitation type on the ground.

Dual-Pol Products & Applications

The base radar products that have been available to users are base reflectivity, base velocity, and spectrum width.  Three new base products will be available after the dual-pol upgrade: differential reflectivity (ZDR), correlation coefficient (CC), and specific differential phase (KDP).  In addition to these three new base products, there will be several derived products.  These include a melting layer (ML) product, a hydrometeor classification algorithm (HCA) product, and eight new precipitation products. 

  • Differential Reflectivity (ZDR): ratio of the reflected horizontal and vertical power returns. Among other things, it is a good indicator of drop shape. In turn the shape is a good estimate of average drop size.
  • Correlation Coefficient (CC): a statistical correlation between the reflected horizontal and vertical power returns. It is a good indicator of regions where there is a mixture of precipitation types, such as rain and snow.
  • Specific Differential Phase (KDP): a comparison of the returned phase difference between the horizontal and vertical pulses. This phase difference is caused by the difference in the number of wave cycles (or wavelengths) along the propagation path for horizontal and vertically polarized waves. The specific differential phase is a "propagation effect." It is a very good estimator of rain rate.

Hover your mouse over the labels below to see examples of the three new dual-pol base products and the HCA product. Images courtesy of the Warning Decision Training Branch.

Differential Reflectivity Correlation Coefficient Specific Differential Phase Hydrometeor Classification Algorithm
Differential Reflectivity


Training & Additional Information

* Information gathered from the WDTB and NSSL (National Severe Storms Laboratory) websites.


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