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<br />3.2 Annual Report 1999 (Matthews et al., 2000) <br /> <br />This GCIP research application effort and the work for the OSF produced a different style of <br />field testing of the SAA under the GCIP program. The algorithm was modified to accept <br />Level m data from NIDS providers in near-real time for a series of five radars across the Dakotas <br />and Minnesota. Products were provided via the Internet in the 4-km HRAP grid so as to be <br />useful for forecast groups. Accumulations of snowfall rate (S) and snow depth (SD) wer,e <br />produced for a variety of time intervals up to 24-hours, ending at 1200 Universal Time <br />Coordinated (UTe) each day. The products of the five radars were combined in a mosaic to <br />show regional accumulations. <br /> <br />Working with the NIDS data was generally successful. The mosaic process indicated that <br />one or two radars appeared to be calibrated differently from the others, as shown by S and <br />SD 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 <br />needs 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 growlth 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 Dlinois. There was insufficient quality data <br />for those 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 <br />clutter. The same products using widespread storm data could be useful in determining <br />adjustments in 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 <br />the 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 e~vents <br />and for a better range correction scheme. <br /> <br />In general, this extension of effort has shown that the original SAA tends to be robust in an <br />operational mode. Therefore, no major modifications to the operational versions of the SAA <br /> <br />8 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br /> <br />I <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />