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<br />140 <br /> <br />JOURNAL OF APPLIED METEOROLOGY <br /> <br />VOLUME 27 <br /> <br />Remote and In Situ Observations of Sierra Nevada Winter Mountain Clouds: <br />Relationships between Mesoscale Structure, Precipitation and Liquid Water <br /> <br />DAVID W. REYNOLDS <br /> <br />u.s. Bu~eau of Reclamation, Auburn, California' <br /> <br />ARUNAS P. KUCIAUSKAS <br />Electronic Techniques, Inc., Auburn. California <br />(Manuscript received 4 March 1987, in final form 5 July 1987) <br /> <br />ABSTRACf <br /> <br />A small subset of mid latitude, midwinter precipitation events affecting the central Sierra Nevada are analyzed. <br />The examples given are representative of60% of the storm types documented during the past 4 yr of the Sierra <br />Cooperative Pilot Project (SCPP). The structure of these frontal systems is consistent with those observed in <br />the United States Pacific Northwest and the British Isles. <br />Combining information from a vertically pointing microwave radiometer, conventional radar, satellite imagery, <br />and detailed time cross sections of rawinsonde data, relationships are developed between these remote sensing <br />devices and the onset of supercooled liquid water (SLW). For the storms described, the highest concentration <br />ofSLW occurs after passage of an upper jet with accompanying upper-level front or surface cold ana- and/or <br />katafront. These frontal pasSages lead to decreasing cloud thickness, warming cloud tops, decreasing precipitation <br />rate, and shallow embedded convection over the Sierra. <br />Disc.ontinuities in cloud top temperature, rainbands, and decreasing echo height, associated with the passage <br />of the upper jet and accompanying front, can be ide~tified with satellite and radar several hours before affecting <br />the Sierra Nevada, thus providing a prediction for the onset or increase in SLW. These relationships have <br />application to wintertime cloud modification programs over the central Sierra. <br /> <br />1. Introduction <br /> <br />The structure and organization of midlatitude syn- <br />optic-scale storms. remains an important area of study, <br />especially with regard to the mesoscale structure of <br />fronts and their effect on cloud precipitation processes. <br />This paper will continue to explore these issues using <br />case study analyses to specifically address three main <br />questions: <br /> <br />l) What are the mesoscale characteristics and frontal <br />structure of certain midlatitude synoptic scale precip- <br />itation systerns affecting the central Sierra Nevada of <br />California, and how do they relate to similar obser- <br />vations in other midlatitude regions? <br />2) How does the structure and organization of these <br />midlatitude systems relate to identifiable features in <br />radar and satellite data? <br /> <br />Corresponding author address: Mr. David W. Reynolds, U.S. Bu- <br />reau of Reclamation, 471 Maidu Drive, Auburn, CA 95603. <br /> <br />1 Storm in this context means a precipitation event induced by a <br />migrating cyclonic system off the Pacific. Storm and precipitation <br />event may be used interchangeably throughout this paper. <br /> <br />3) What relationships exist between storm structure <br />and organization and precipitation processes occurring <br />within the cloud systems? Specifically, what regions <br />within the storm have clouds containing excesses in <br />supercooled liquid water (SL W)? <br /> <br />As regard questions 1 and 2, recent studies by <br />Browning and Monk (1982) and Browning (1985) have <br />formulated conceptual models as a basis for analysis <br />of cold fronts. This work built largely on earlier studies <br />by Bergeron (1937) who classified cold fronts into two <br />distinct categories, anafront and katafront. A cold ana- <br />front is characterized by air within the warm sector <br />rising ahead of and over the cold front since the cold <br />front moves faster and overtakes the warrn air. A cold <br />.katafront is characterized by general subsidence of the <br />warm air with low relative humidities in the mid and <br />upper levels as the cold front lags the motion of the <br />warm air. Sansom (1951) suggested that cold anafronts <br />and katafronts are closely tied to the stage of storm <br />development, anafronts being associated with the de- <br />veloping stage, and katafronts with the dissipating or <br />occluding stage. <br />With regard to question 3, Hobbs (1978) looked at <br />both the mesoscale organization of cyclonic storms as <br />well as the rnicrophysical processes occurring within <br />