WMOD00548 - Laserfiche WebLink

Home Browse Search

32 4.4 8-9 February 1978 CASE STUDY Atmospheric circulation was very strong in the Pacific during the \ second week of February. A deep low pressure system at 70 kPa moved southward from the Gulf of Alaska and passed over California between i '# ! 0000 GMT and 1200 GMT on 9 February. The long wave trough at 20 and 30 kPa deepened off the west coast of the u.S. and heavy rains with flooding and mud slides occurred in southern California in the days following the Sierra storm. Extensive thick cirrus on the southeast side of the long wave trough covered the target area over the lifetime of the storm, reducing the usefulness of satellite observations for identification of mesoscale features in the clouds. The 2245 GMT, 8 February visible image, Figure 14, shows the large areal coverage of upper level cloudiness preceding ~ the trough. o CTT was around -40 C over the target at this time (Figure 15). From the 0000 GMT, 9 February sounding at Sheridan, the tops of -:.. upper level clouds were near 30 kPa. Winds at this level were from o -1 ~240 at 94 ms . The high speed of the cirrus imbedded in the upper level jet was the most obvious feature seen in the satellite image 'loops displayed on the ADVISAR. University of Wyoming aircraft observations between 1910 and 2220 GMT reported overcast skies above the low-level clouds, and no attempt was made to fly to the upper deck. Lower clouds were thus effectively blocked from the satellite view, with a gap between cloud layers from 85 to 53 kPa observed on the 2100 GMT, 8 February Sheridan sounding. Precipitation began around 0000 GMT on 9 February at the mountain stations (Figure 16) and rain was reported at Sheridan, where a marked .., change in the sounding at this time took place. The gap between low