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<br />Supercooled water increased substantially after the passage of the cold- <br />frontal rainband. The radiometric measurements contained many peaks typical of <br />convectivE~ cloups. B~ 0330 on 25 flebruary, only a shallow no.nprecipitat~ng <br />6~bgraphit ~loud remained. This cloud system' remained over the Sierra Nevada <br /> <br />for nearly 12 hours before dissipating. Supercooled water was present continu- <br /> <br />ously in this cloud in quantities from 0.20 to 0.50 mm. Satell ite photographs <br /> <br />and radiometric data suggested that convection weakened in intensity with time <br /> <br />and that an orographic cloud remained over the Sierra Nevada crest. <br /> <br />Discussion <br /> <br />The 23-25 February storm was one of 12 storm systems where the center of the <br /> <br />storm was occluded, near the coast and north of 420 latitude. At the latitude <br /> <br />of the project area, the storms occurred in association with the passage of a <br /> <br />cold front. The duration of precipitation at higher altitudes was generally <br />10 to 15 hours, although cloud cover was often present for 24 to 48 hours. In <br />general, the cold front was preceded by a wide cirrus shield. The back edge of <br />the cirrus shield was often, but not always aligned with the upper troposphere <br /> <br />" <br /> <br />jet axis. Depending on the evolution of the storm, this axis, and the cirrus <br /> <br />boundary was either aligned with or east of the surface cold front. The latter <br /> <br />case was more common. The cloud systems associated with the fronts followed <br /> <br />this typical evolution: Cirrusfir'st moved over the region. low level clouds <br />developed rapidly and precipitation began to fall as the front approached. A <br /> <br />very distinct cold frontal rainband moved through the Sierra Nevada within a few <br />hours after the onset of precipitation. After the rainband passed precipitation <br /> <br />- <br />rates reduced substantially and shallow convective cells developed over the <br />foothills and higher Sierra Nevada. These cells were often embedded in an <br /> <br />orographic cloud. <br /> <br />16 <br />