OCR Text |
Show -15°C isotherm was located near 12, 000 ft. MSL during the morning, lowering to 11, 000 ft. MSL on the 1153 MST and 1603 MST soundings. Moist adiabatic stratification prevailed at 0503 lV[ST (allowing possible cumulus tops to -20°C), but the three subsequent soundings were stable. 4. 5. 3. 1. 2 Seeding Schedule Silver iodide was released for one hour from Mt. Harris beginning at 0500 MST and again at 1400 MST. 4. 5. 3. 1. 3 Computed Trajectories and Resulting Seeded Precipitation Fallout Areas Figures 111 and 112 show the interception of the computed seeded crystal trajectories with the ground. The vertical profiles of wind used to compute these trajectories are shown in Figures 105 and 106 and the numerical model computed orographic vertical velocity fields are presented in Figures 113· and 114. The predominant seeding effect from the first seeding event should have occurred over the southern half of the target area between 0630 and 0830 MST, while the second period seeding effect should have been mostly between 1500 and 1 730 MST over all but the northern edge of the target. 4. 5. 3. 1. 4 Precipitation Rate Characteristics Figure 115 shows the optical snow-rate sensor records for selected stations, along with the computed hour of expected maximum seeding effect. Buffalo Pass and Fish Creek were located north of the computed seeding effect from the 0500 lV[ST Agl release and their precipitation rates do not show a maximum as the seeding effect crossed the ridge. Stations in the path of the seeding do show rate increases in good agreement with the computed time of effect. There is physical evidence in the form of silver-in-precipitation measurements and replica analysis that seeding was responsible for these increased rates. Rate changes due to the second seeding release at 1400 MST were obscured in a more complex precipitation pattern. Hourly totals from weighing bucket records are shown in Figures 116a through 116f. These r e cords, too, reflect the seeding effect from the 0500-0600 MST release. 4. 5. 3. 1. 5 Silver-in-Precipitation (AAS Values) The time histories of atomic absorption spectrophotometer silver-in-precipitation concentrations obtained from snow samples collected at Emerald Mountain and Rabbit Ears Pass are shown in Figures 117 and 118. The history at Emerald Mountain reflects the passage of both p e riods of s e eded pre- 181 |