![]() Weather radars can also pick up returns from nearby objects on the ground (ground clutter) and flying insects. So, rain will occur in some places (such as the western side of the Olympic Mountains) without it showing up on our loop. The beam can be blocked by mountains, and some areas are simply too far away from any radar. The coverage of the Pacific Northwest by weather radar is by no means uniform. Our loop shows the signals recorded by several radars in the northwest over the last several hours. High values of dbz (color scale to the right of the image) indicate large drops and heavy precipitation. Raindrops and snow produce reflections that become stronger as the size of the drop or flake increases. ![]() The reflectivity and velocity data from the WSR-88D are the primary data sources that National Weather Service meteorologists use to issue short-fused warnings for tornadoes, severe thunderstorms, and flash floods.Weather radars send out pulses of microwave energy and listen between the transmitted pulses for part of that the energy to be reflected back to the radar. The sophisticated computers within NEXRAD analyze these frequency shifts which can then be displayed as color imagery on the AWIPS workstation. ![]() The speed is determined by the amount of this frequency shift. If the wind is moving precipitation away, the frequency of reflected energy decreases. If wind is moving precipitation toward the radar, the frequency of reflected energy picked up by NEXRAD increases. The Doppler effect is the alteration of the frequency of the radar-transmitted pulse of energy at the moment it is reflected off of a moving target (precipitation). NEXRAD determines the movement of wind-driven precipitation using a principle known as the "Doppler effect". Forecasters use other information at their disposal to make this determination. In addition, radar alone cannot determine if precipitation is rain or snow. There is no reason for the weather to surprise you anymore, with up to 12 hou. The radar is so sensitive that it can detect clouds, dust and aerosol particles, insects, and birds, not to mention airplanes and ground based objects near the RDA itself. The NOAA Radar and Weather Forecast app offers you the best radar map available on the store with more than 35 real-time and hyper accurate weather layers to choose from in order to plan your perfect day, week or vacation. Unfortunately, the radar can display "echoes" that may or may not represent meteorological targets. The most common is a reflectivity image, which shows the areal extent of precipitation. The Advanced Weather Interactive Processing System (AWIPS) workstation, allows forecasters to display radar data(top picture). The processing computer, known as the Radar Product Generator (RPG), performs various data quality checks of the raw radar data and creates radar images and products. The returned energy, called base data, is sent from the RDA site to the processing computer located here in the office(bottom picture). Part of the energy will be reflected back to the antenna, where the dish focuses the returned energy. When this energy hits an object, like a raindrop or snowflake, it is reflected in all directions. The transmitter at the antenna within this protective dome sends out a pulse of energy. The radar dish (pictured above) is protected by a covering that resembles a giant soccer ball. It all starts at the Radar Data Acquisition unit (RDA), which is the tower (pictured above) located adjacent to the forecast office. Radar requires three integral parts to work: (1) an antenna/receiver, (2) computers that process the raw radar data, and (3) an interactive workstation that the forecasters can use to display the processed radar data. The term WSR-88D is simple to explain: WSR stands for Weather Surveillance Radar 88 represents the year the first NEXRAD was commissioned for use (1988) and the D means it is a Doppler radar. Within the National Weather Service, NEXRAD is officially called the WSR-88D. In this way, the radar images can be shared with all interested groups. News agencies, television stations, military installations and other sites have access to the radar images through cooperation with the National Weather Service. The National Weather Service's Doppler radar, known as NEXRAD (for the NEXt generation of RADar), is the only Doppler weather radar on Long Island.
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