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<br />. <br /> <br />. <br /> <br />. <br /> <br />Summary and Discussion <br /> <br />This GCIP research application effort and the work for the OSF produced a different style of field <br />testing of the SAA under the GCIP program. The algorithm was modified to accept Level III data <br />from NIDS providers in near real time for a series of five radars across the Dakotas and <br />Minnesota. Products were provided via the Internet in the 4-km HRAP grid so as to be useful for <br />forecast groups. Accumulations of Sand SD were produced for a variety of time intervals up to <br />24-hours, ending at 12 UTC each day. The products of the five radars were combined in a mosaic <br />to show regional accumulations. <br /> <br />Working with the NIDS data was generally successful. The mosaic process indicated that one or <br />two radars appeared to be calibrated differently from the others, as shown by Sand SD <br />discontinuities across lines equidistant between the radars. <br /> <br />Virga was a persistent problem. An experimental procedure eliminated most virga without <br />sacrificing the reliability of the algorithm in widespread, intense storms. That algorithm still needs <br />further testing and adjustment before becoming part of the operational version of the SAA. <br /> <br />The SAA failed to match surface observations during a snowstorm in arctic air. An analysis <br />indicated that the storm was shallow and had temperatures in the dendritic growth band for snow <br />crystals. The radar beam generally was above the clouds, missing the rapid crystal growth close <br />to the ground. Furthermore, dendritic crystals have the least density as snow on the ground. A <br />change in a few adaptable parameters could have remedied the problem, but such was not <br />possible in the routine production of products from the NIDS data stream. <br /> <br />Though desired in the specifications for tasks, it was not possible to derive local parameters of <br />alpha and beta for radars in Alaska, Washington, and Illinois. There was insufficient quality data <br />forthose sites. Analyses of the California (Sierra Nevada) data indicated that the radar beam was <br />far above the snow growth zones, which resulted in small alpha values. <br /> <br />A separate program was written to combine many days of SAA files to produce composite accu- <br />mulations for three partitions of area coverage: scattered, moderate, and widespread. The output <br />gave guidance for adjusting the hybrid scan file for inadequate or excessive suppression of clutter. <br />The same products using widespread storm data could be useful in determining adjustments in <br />the occultation correction file. <br /> <br />As part of the virga investigations, experimental coding was produced to generate images of the <br />vertical profile of reflectivities. The images gave insights into the changing vertical structure of the <br />storms. Parts of the code could be used for producing a better algorithm that is sensitive to <br />vertical gradients. There is potential for better performance with virga and bright band events and <br />for a better range correction scheme. <br /> <br />In general, this extension of effort has shown that the ol;ginal SAA tends to be robust in an oper- <br />ational mode. Therefore, no major modifications to thl3 operational versions of the SAA were <br />made. There are lingering blemishes to work on, such as virga and bright band effects, but for <br />now, forecasters can be alerted to their effects by the natures of the patterns (rings and intense <br />gradients) in the SAA output. <br /> <br />7 <br />