At 1445 LT, Texas A&M University meteorologists called the Bryan Police Department and forecast that a tornado would touch down 30 min. The Texas A&M University radar observed strong, tall, hook-shaped echoes with V-notch signatures after 1400 LT. At noon that day, the Weather Bureau Forecast Center at Kansas City, Missouri, had issued what we would today call a tornado watch for an area just to the north of Bryan. On 5 April 1956, a tornado that produced damage in Bryan and College Station, Texas, was detected by the Texas A&M University radar. "The modified APS-2F at Texas A&M University, although not formally a part of the Texas Tornado Warning Network, was used at least once for warning purposes (Bigler 1956). The AN/CPS-9 model was the first purpose-built weather radar. Using this 3-cm radar, researchers studied mid-latitude mesoscale systems, severe storms, and land-falling cyclones. In the early 1950s, the department received a 3-cm weather radar, AN/CPS-9, from the US Air Force. A final upgrade to the pedestal, removal of the side dishes, new processor, and work station occurred in 1997. In 1992, the Aggie Doppler RADar was born with the installation of doppler capability. After several modifications, the radar was placed on top of the newly completed Eller O&M Building in 1973. In 1962, they upgraded to a 10 cm, and in 1966, dual wavelength capability was added. The Meteorology department first began its study of convective storms with the use of a 3 cm wavelength radar in the early 1950s. The Aggie Doppler Radar ( ADRAD) is a Doppler weather radar located on the roof of the Eller Oceanography & Meteorology Building on the Texas A&M University campus in College Station, Texas. Since hail can cause the rainfall estimates to be higher than what is actually occurring, steps are taken to prevent these high dBZ values from being converted to rainfall.The current Aggie Doppler Radar dish The Aggie Doppler Radar in operation atop the Eller O&M Building at Texas A&M University during a rare southern Texas snow storm on February 23, 2010 Hail is a good reflector of energy and will return very high dBZ values. These values are estimates of the rainfall per hour, updated each volume scan, with rainfall accumulated over time. Depending on the type of weather occurring and the area of the U.S., forecasters use a set of rainrates which are associated to the dBZ values. The higher the dBZ, the stronger the rainrate. Typically, light rain is occurring when the dBZ value reaches 20. The scale of dBZ values is also related to the intensity of rainfall. The value of the dBZ depends upon the mode the radar is in at the time the image was created. Notice the color on each scale remains the same in both operational modes, only the values change. The other scale (near left) represents dBZ values when the radar is in precipitation mode (dBZ values from 5 to 75). One scale (far left) represents dBZ values when the radar is in clear air mode (dBZ values from -28 to +28). Each reflectivity image you see includes one of two color scales. The dBZ values increase as the strength of the signal returned to the radar increases. So, a more convenient number for calculations and comparison, a decibel (or logarithmic) scale (dBZ), is used. Reflectivity (designated by the letter Z) covers a wide range of signals (from very weak to very strong). "Reflectivity" is the amount of transmitted power returned to the radar receiver. The colors are the different echo intensities (reflectivity) measured in dBZ (decibels of Z) during each elevation scan.
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