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<br />FEBRUARY 1988 <br /> <br />DA VID W. REYNOLDS AND ARUNAS P. KUCIAUSKAS <br /> <br />149 <br /> <br /> <br /> <br />':> <br /> <br />transition to heavily rimed dendrites, needle aggregates, <br />and large frozen water drops. Note from Figs. 7c and <br />8b that the radar echo height and CTT both indicate <br />the colder deeper cloud remaining over the barrier after <br />both these features passed. This upper cloud was sep- <br />arated microphysically from the lower cloud over the <br />valley but merged with the orographic cloud over the <br />barrier just to the west of Blue Canyon (Fig. 10). It is <br />hypothesized that the mid- and upper cloudiness re- <br />mained due to the interaction of the frontal band and <br />the short-wave trough aloft. A small-scale comrna <br />shaped cloud feature can be observed in association <br />with this interaction over the central valley of Cali fomi a <br />in Fig. 8b. <br />After the cold katafront passed, decreasing wind- <br />speeds in the lowest 1-5 km reduced the CSR. In ad- <br />dition, ice concentrations generated by the upper cloud <br />deck, along with needle production in the lower cloud <br />deck, were sufficient to remove a substantial portion <br /> <br />I <br />~ <br /> <br /> <br />FIG. 8. Sequence ofGOES-W satellite images for 24 March 1985. <br />Gray-scale enhancement as in Fig. 3. Location of surface front an- <br />notated. (a) 1831 I-km resolution visible image with CTT < - 300C <br />inserted. (b) As in (a) except 2131 image. (c) 0101 25 March 8 km <br />resolution infrared satellite image with CTT < - 300C gray scaled. <br /> <br />of the lower cloud's SLW. It was not until the upper <br />cloud moved to the east after 0000 (Fig. 9c), that pre- <br />cipitation rates decreased to less than 0.5 mm hr-I and <br />SL W within the remaining shallow orographic cloud <br />recovered substantially, even though CSR decreased <br />substantially. Note again that the back edge of this <br />rniddle cloud deck is associated with an upper-level jet <br />passage which is accompanying the main upper-level <br />baroclinic zone. <br />In summary, this case study has again shown that <br />the passage of an upper-level jet and accornpanying <br />cold surge/cold katafront changed the precipitation <br />process from a predominately seeder-feeder mecha- <br />nism with clouds containing little SLW by removing <br />. the seeder cloud. The low-level clouds rernaining pro- <br />duced very low precipitation rates and contained sig- <br />nificantly more SLW. In this case the interaction of an <br />upper short-wave trough and the cold katafront rnain- <br />tained mid- and upper-level clouds several hours past <br />