new systems are the Advanced Weather Interactive Processing System (AWIPS)1 and the Integrated Terminal Weather System (ITWS). AWIPS is a modern data acquisition and distribution system that gives meteorologists singular workstation access to NEXRAD radar products, satellite imagery, gridded weather forecast data, point measurements, and computer- and man-made forecast and warning products. The result is an integrated forecasting process that utilizes a comprehensive set of data for application by National Weather Service (NWS) Offices and others to generate more accurate and timely weather forecasts and warnings (Facundo, 2000). ITWS combines data from a number of weather radars, including NEXRAD, the Terminal Doppler Weather Radar (TDWR), and airport surveillance radars (ASR), with lightning cloud-to-ground flash data and automated weather station measurements to produce a suite of products that display current weather as well as nowcast weather out to around one hour for use by air traffic controllers in the management of airport terminal operations (Evans and Ducot, 1994).

The evolution of weather radar in the United States has been marked by the development and implementation of a series of operational systems, including the CPS-9, the WSR-57, and the WSR-88D (NEXRAD). Each of these systems was a response to the recognition of new needs and opportunities and/or deficiencies in the prior generation radar. The CPS-9 (X-band or 3-cm wavelength) was the first radar specifically designed for meteorological use and was brought into service by the U.S. Air Force USAF Air Weather Service in 1954. The WSR-57 was the radar chosen for the first operational weather radar system of the NWS. It operated at S-band or 10-cm wavelength, chosen to minimize the undesirable effects of signal attenuation by rainfall experienced on the CPS-9 3-cm wavelength radar. The development of the WSR-88D was in response to demand for better weather information and resulted from advances in Doppler signal processing and display techniques, which led to major improvements in capabilities of measuring winds, detecting tornadoes, tracking hurricanes, and estimating rainfall. These remarkable new measurement capabilities were a direct consequence of many engineering and technological advances, primarily advances in integrated circuits, digital signal processing theory, and display systems, and these advances led to advanced research weather radars. Radar meteorology research has also played a critical role in these developments through the generation of new knowledge of the atmosphere, especially regarding cloud and precipitation physics, severe storm evolution, kinematics of hurricanes, and detection of clear air phenomena such as gust fronts and clear air turbulence. Such knowledge has greatly benefited the operational utility of weather radar, particularly through innovations, understanding, and testing of algorithms that process radar data into meaningful physical descriptions of atmospheric phenomena and weather con-

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A complete list of acronyms and their definitions is provided in Appendix B.



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