Update: Dual-Polarization Upgrade to NWS Chicago Doppler Radar - October 17-30

The National Weather Service (NWS) Chicago Forecast Office is very pleased to announce that the much-anticipated installation process of the Dual-Polarization Radar upgrade to the KLOT WSR-88D will finally occur between October 17th and October 30th 2011. This timeframe for installation is seen as a firm date, but should any last minute changes occur, the page will be updated once again.  NWS Chicago will be one of the first NWS offices in the country to receive this important technology, which will greatly expand the amount of data types and radar products available to users.  It is also important to note that the radar will be offline during the entire 2 week period of installation.

Conventional Doppler radars transmit bursts of radio waves, called pulses, in a single, horizontal orientation, or polarization. The pulses bounce off meteorological (i.e. clouds, snow, ice pellets, hail and rain drops) and non-meteorological (i.e. birds, insects, ground clutter, including wind farms etc.) particles in the atmosphere, and are reflected back to and received by the radar dish.  After computer processing, the returned signals are converted into usable data regarding the horizontal properties of the particles encountered, including their dimensions and direction and speed of movement.  For instance, the distance from the radar to the target is calculated from the amount of time that lapses from the initiation of the pulse, to the detection of the return signal.  The radar reflectivity you see on a radar image is actually the “reflected” pulse energy that is received by the radar. 

Dual-polarization, or Polarimetric, radars transmit and receive both horizontally and vertically oriented radio wave pulses, typically done by alternating between horizontal and vertical polarization with each pulse.  This therefore allows the radar to collect data with information on the horizontal and vertical properties of the targets.  Being able to analyze targets in this manner is expected to result in significant improvements in the estimation of precipitation rates, the ability to discriminate different precipitation types (i.e. rain vs. hail, mixed precipitation types in winter storms), and the identification of non-meteorological returns. As an added example, for aviation concerns, with polarimetric radar, forecasters will be able to better discern areas of icing and other hazards such as birds.  All these improvements will aid forecasters in the warning decision process, helping the public make better decisions about their safety and protecting their property.

The basic radar products that have been available to users are Z, reflectivity (base and composite), V, mean radial velocity (base and storm relative), and SW, spectrum width.   Three new products that will become available after the upgrade are ZDR, differential Reflectivity, CC, correlation coefficient, and KDP, specific differential phase. Below is an example of Differential Reflectivity on the left, versus reflectivity on the right.  The area circled on both images is a hail core in a thunderstorm, demonstrating how Differential Reflectivity can allow for better discrimination of hail from just heavy rainfall.  Along with the three base products above, included among three new derived products will be Quantitative Precipitation Estimation (QPE), which will allow for the estimation of instantaneous rainfall rate.  Currently, only 1-hour radar-based rainfall rate estimations are available.

Dual-Polarization Radar Outreach Training has been made available by the NWS Warning Decision Training Branch (WDTB). This training, with separate tracks for meteorologists and non-meteorologists, is targeted at first responders, broadcast meteorologists, other private sector meteorologists, emergency managers and other public stakeholders, and can be accessed from this link.

For more in-depth information regarding the radar upgrade, we encourage you to refer to the following links:

Dual-Polarization PowerPoint by Meteorologist in Charge Edward Fenelon (7.71 MB)

Adobe Reader PDF of Fenelon's Presentation (1.88 MB)

Dual-Polarization PowerPoint by Senior Forecaster Mark Ratzer (8.46 MB)

Adobe Reader PDF of Ratzer's Presentation (1.41 MB)

Polarimetric Doppler Radar by NOAA's National Severe Storms Laboratory 

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