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Last modified
7/28/2009 2:41:49 PM
Creation date
4/30/2008 2:42:19 PM
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Template:
Weather Modification
Title
Investigations of Winter Storms over the Wasatch Plateau during the 1994 NOAA-Utah Field Research Program - Final Report
Date
7/1/1996
State
UT
Weather Modification - Doc Type
Report
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The first seeding experiment of the 1994 field season was conducted on this day, with silver <br />iodide and SF:, released from the n\'o high altitude seeding sites between about 1045 and 1545 (see <br />Fig. 7). The ~'ISU manual generators were used for the silver iodide seeding. Although much of the <br />CSBR radiometer data were missing for the seeding period, there were occasional icing counts at <br />RRS, and mobile radiometer data (not sho\\n) indicated SL \V depths from 0.03 to 0.10 mm during <br />the seeding period. Figure 7 shows that at least one of the seeding aerosol plumes was over RRS for <br />about four hours. Heimbach ( 1994) discusses the research aircraft flight which took place from 1100 <br />to about 1430. Precipitation was very light during the seeding experiment. At TAR three snow <br />samples were collected benveen 1120 and 1600, each indicating an average precipitation rate of 0.25 <br />to 0.30 mm h-i, fur a total of about 1.2 mm. <br />This first case showed the importance of the local topography and its influence on the <br />airflow. There were no frontal features influencing cloud development over the Wasatch Plateau. In <br />fact the upper level synoptic pattern suggested little opportunity for upslope conditions existed on <br />the western slopes of the plateau. However, the position of the surface low in combination with the <br />orientation of the local mountains led to a weak orographic cloud situation \...ith some potential for <br />modification by cloud seeding. The possibility of interaction between cold seeder clouds and the <br />shallow orographic layer existed, but the satellite images indicated the colder clouds gradually <br />moved to the east as the day progressed. <br /> <br />B. 7-8 February 1994 Storm Period <br />The 7-8 February storm developed over the research area as a deep trough in a southern <br />branch of the westerlies moved through southern California and Arizona, at the same time that a <br />series of short waves in the northern branch of westerlies moved southward out of Canada into Idaho <br />and Ctah. The advection of warm moist air over Utah from the southwest began early on 7 February, <br />and by 0500 the dew point depression at 700 mb had decreased to 3" with the temperature at - 80 <br />(over central Ctah). Figure 8 shows the cloud field and 700 mb data at this time. Clouds over the <br />research area were relatively warm topped, vyith the main field of colder-topped clouds being to the <br />south over Arizona. <br />Over the period from 0500 to 1700 on 7 February warm advection increased the 700 mb <br /> <br />15 <br />
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