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152 JOURNAL OF APPLIED METEOROLOGY VOLUME 27 l3 shows a distinct transition in CTT passing through Kingvale between 0100 and 0200 with colder cloud tops to the south and east.. This drop in cloud tops can also be seen in the decreasing echo heights at this tirne (Fig. 11 c). The mesoscale circulation associated with the upper and lower jet couplet may have initiated this rainband and is depicted in Fig. 12a at 0 100 as band No. 1 with the back edge near Auburn and Blue Canyon. The cold anafront passage (rainbandNo. 3) was pre- ceded by a separate rain band which is labeled in Fig. 12 as NO.2. The mechanism of its formation is un- known. Rainband No.3 can be interpreted as a narrow cold frontal rainband and was distinctly convective in nature. None of the three bands was observed to con- tain substantial SL W by the radiometer as they passed the crest. However, indications frorn the ice crystals observed at Kingvale showed higher liquid water con- tents were available for crystal growth, since graupel, large frozen water drops, and an abundance of needles were noted as each band passed Kingvale. It appears that riming, coalescence, and needle production effec- tively utilized additional condensate produced in the bands~ With passage of the cold anafront through KGV between 0400-0500, SL W increased and precipitation rates dropped. The airmass behind the front was po- tentially unstable. The release of this instability, through fQrced ascent over the barrier, could be seen in the. embedded convection which developed in the remaining orographic cloud and'gave rise to large fluc- ~ tuations in SL VI amounts. This SL W lasted until an increase in low- and mid-level moisture, associated with . the main upper-level trough, began moving over the area, enhancing the orographic cloud and increasing precipitation. In summary, this case has shown that for this well- defined cold anafront and associated warm front, the precipitation mechanism was very efficient in removing any excess SL W due mostly to the strong vertical mo- tion field accompanying a very intense upper-level jet. It was not until after the cold anafront passage that SL W above Kingvale increased substantially, owing to convection and the decrease in precipitation rate due to the loss of the deep colder cloud. 4. Summary and conclusions Three main questions were asked in the Introduc- tion. The first question addressed the structure and or- ganization of storms affecting the central Sierra Nevada and relationships of these to other geographical loca- tions. Analysis of the frontal characteristics for the three' . storms presented here could be performed within the framework of the conceptual models of Hobbs (1978) and Browning (1985). Thus, the present study helps to substantiate these conceptual models and clarifies, to some extent, the important role of these frontal features to the precipitation process. For the three cases pre- sented it appears that forward sloping ascent of the warm conveyer belt (warm frontal overrunning) pro- duced the bulk of the precipitation and made two of the three events significant precipitation producers. A seeder-feeder mechanisrn was the dominant mecha- nism of preCipitation production during this stage of the storm. Precipitation associated with cold kata- or anafronts is usually intense (4-8 mm h-1) but short- lived. Riming growth is significant in these regions as well as an abundance of warm crystal habits such as needles. Passage of upper-level fronts or baroclinic re- gions with an associated jetstreak have been shown to induce rainbands, but are followed by decreasing cloud tops and normally decreasing precipitation. Again, riming and needle production are significant contrib- utors to precipitation in, this region. It is the passage of these upper-level features that can be related to distinct discontinuities in satellite and radar imagery and provide an answer to the second question. Based on the accuracy .with which 3-h soundings can identify upper jets or jet streaks, the case studies presented show a fairly close relationship between the passage of an upper jet imd a distinct dis- continuity in CTT, as seen on satellite irnagery and in both radar reflectivity and radar echo height. It is these upper-level baroclinic regions and associated jets that induce vertical circulations giving rise to upper-level cold surges/humidity fronts and cold ana- or katafronts (Keyser and Shapiro, 1986). The final question addressed relationships between storm structure and excesses in cloud SL W as could be observed near the crest of the Sierra Nevada. These three cases have shown three specific regions within a precipitation system in which excesses'in SL W might exist. The first is in the leading edge of the event, when mid- and low-level moisture. begins advectiIig in over the barrier or over a preexisting stable layer. This SL W exists prior to the onset of precipitation. The second period is behind the passage of an upper cold surge/ humidity front. If these occur ahead of the low-level cold front, their passage temporarily reduces ice crystals generated from aloft, thus interrupting the natural seeder-feeder mechanism. The drying aloft increases potential instability thus increasing embedded convec- tion within the cloud. The third region is behind a cold anafront. Here again the upper-level cloudiness is re- moved via subsidence, thus removing the natural seeder mechanism. Low- and midlevel potential instability increases due mainly to the very dry air which overrides the shallow moist zone over the barrier. As air parcels are forced to ascend over the Sierra Nevada, the po- tential instability is realized in the form of embedded convection within the orographic cloud. Thus, although CSR decreases along with precipitation rates local pro- duction of condensate via embedded convection, pro- vides increases in SL W within the shallow cloud. 'Each of these three specified regions is associated with a discontinuity in CTT as seen from satellite and, with a discontinuity in radar reflectivity and echo 'I 1 'I 1