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<br />A closed circulation center at 50~ mb was present over the east Pacifit near <br /> <br />Washington at 1200 on 24 February. A deep, 984 mb surface low was centered off <br /> <br />the coast. The .cloud field associated w.ith this system wrapped around the <br /> <br />. . <br />. . <br />~enter of cirtulatidn, a pattern typical of many deep occlusions. <br /> <br />The thermal structure and moisture fields associated with the cold frontal <br /> <br />system on 24 February were very similar to the split front model discussed by <br />Browning and Monk (see Reynolds, 1986). The storm system was preceded by a wide <br />cirrus shield. The cirrus clouds were located on the anticyclonic side of the <br /> <br />jet. The back edge of the cirrus shield was aligned very closely with the jet <br /> <br />core in the upper troposphere. An upper-level baroclinic zone was present near <br />the jet core. This zone marked the boundary of subsiding air on the cyclonic <br /> <br />side of the jet. Low-level moisture was first observed to move into the lower <br /> <br />Sierra foothills around 1200, approximately 8 hours ahead of the surface front. <br /> <br />The top of this moist layer was confined by the subsidence inversion. Based on <br /> <br />satellite photographs and rawinsonde data, the passage of the jet core and onset <br /> <br />of low level moisture occurred at approximately 1500 at Kingvale, in association <br /> <br />. . <br />\'Jith the formulation of an orographic cloud. Weak embedded convection occurred <br />withi n the system associ ated with 'v,reak convecti ve i nstabi 1 ity near cloud top <br /> <br />(Huggins et al., 1986). Supercooled water measurements had a steady background <br />value of 0.05 m~ with peaks from 0.20 to 0.50 mm. Precipitation was steady at <br />2 mmh-1 for approximately 5 hours. The cloud system began to dissipate over <br />Kingvale at 2030. The surface front passed Sheridan at 2000 and Kingvale at <br />2300. At 2230, a weak cold frontal rainband associated with the surface front <br />moved through Kingval~. Precipitation rates increased to 4 mmh-1. The cloud <br /> <br />system became much more convective. .' Convective cells continued to develop for <br /> <br />several hours producing rain and snow showers through the Sierra Nevada. <br /> <br />15 <br /> <br />. --- :.. ~- :j <br />