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<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 /> <br /> <br />Figure 11. - Height contour pattern at the 500 millibar pressure level 24 <br />hours after that in figure 10. <br /> <br />Similar to the B-1 system, identified here as B-2, a pattern develops which is <br />characterized by the presence further east of the cold, closed-circulation <br />low in Canada (figu res 12 and 13). Weak 1,I:Jtl-pressure waves survi ve the <br />passage across the southern portion of the high-pressure ridge which is <br />located to the west of the Canadian low. These transient waves will amplify <br />somewhat after moving past the high-pressure ridge and lead to a 1-2 day, <br />intennittent precipitation event over Arizona. High pressure invades the U.S. <br />through the northern High Plains. The surface cold front trails southward <br />from a weak Great Basin cyclone that moves slowly eastward. <br /> <br />Undoubtedly, other synoptic types exist at times. However, the four described <br />appear to occur most frequently and account for a substantial amount of the <br />wintertime Arizona mountain precipitation. <br /> <br />24 <br />