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Show a geostrophic west to west southwest flow was evident (Figure 172). There were no fronts or short wave troughs in the vicinity Thus, precipitation was purely orographic character and mostly confined to ridge stations. O The ML Harris 1 703 MST sounding (Figure 173) indicated an orographic cloud between 640 mb (12, 000 ft. MSL and -13°C) and 425 mb (22, 000 ft. MSL and -33 °C). Slightly unstable lapse rate prevailed up to 470 mb, which would 'l, support weak convective precipitation elements. !. 4. 5. 4. 2. 2 Seeding Schedule Agl wing flares (on a WSI aircraft >:~ ) were burned along a predetermined track at 11, 500 ft. MSL for six minutes from 163 5 to 1641 MST. 4. 5. 4. 2. 3 Computed Trajectories and Resulting Seeded Precipitation Fallout Area Figure 174 shows the computed vertical dispersion of the Agl release, along with fallout trajectories of seeded snow crystals initiated at selected cloud temperatures. Figure 1 75 shows trajectory intercepts with the ground, and the envelope enclosing them which comprises the computed seeded precipitation fallout area. This indicates that all of the target area was seeded. . 4. 5. 4. 2. 4 Precipitation Rates Figure 1 76 shows time histories from optical snow rate sensor records and the computed hour of maximum expected seeding effect. While some snow was already occurring on the ridge crest prior to seeding, rates increased decid·edly in a very good timing agreement with the arrival of seeding effect. In fact, it appears that seeding was responsible for initiating snow at False Top (on the upwind edge of the ridge) and Columbine Lodge (downwind from the crest). Even though seeding material was released for only a few minutes; experience has shown there is frequently a lingering seeding effect for several hours. From Figure 176, this apparently occurred in this case. Precipitation totals were light in accord with a rather weak orographic vertical ,. velocity field. 4. 5. 4. 2. 5 Silver-in-Precipitation Three snow samples taken at Buffalo Pass during the afternoon were analyzed for silv e r c ontent. The sample including the computed hour of expected ma.xi>:~ w e a ther Science Incorpo r ate d, Norman , Oklaho ma 254 |
