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<br />A third prominent type, called B-1, is characterized <br />by the presence of a closed quasi-stationary upper air circulation <br />over western Canada with a trough over the Rockies and the <br />western Great Plains. Short wave troughs move from the northwest <br />around the low, passing through Arizona, bringing intermittent <br />precipitation which lasts 1-2 days. Precipitation generally <br />ranges from light to moderate amounts. <br /> <br />The fourth weather type, identified as B-2, is similar <br />to the B-1 system and generally differs in that the closed- <br />circulation in Canada is further east than with B-1 and the <br />upper flow is more zonal. Weak low-pressure waves pass across <br />the southern portion of a high pressure ridge (west of the <br />Canadian low) amplifying somewhat after passing through the <br />ridge. <br /> <br />The Medina report offered an estimate of the modification <br />potential of each of the four weather types identified as <br />being the most frequent. Based on the fact that the A-1 type <br />leads to deep cold clouds, which are frequently naturally <br />more efficient precipitation producers, it was concluded that <br />this type possesses less potential for augmentation than does <br />the A-2 type, which is usually a less efficient precipitation <br />producer. This is because the A-2 type has less moisture <br />available and generally is accompanied by somewhat warmer <br />air. The relative potential was rated low for A-1 and low <br />to moderate for A-2. <br /> <br />The B-1 system was judged to be sufficiently wet and <br />cold to have a moderate to high augmentation potential. The <br />B-2 type, generally warmer than B-1, was considered to have <br />a low to moderate potential. Both types of storm systems <br /> <br />3-5 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />